Systematic Review on the Efficacy, Effectiveness, Safety, and Immunogenicity of Monkeypox Vaccine

Background: The variation in the reported vaccine safety and effectiveness could contribute to the high rates of vaccine hesitancy among the general population and healthcare workers in areas where monkeypox (mpox) is circulating. In this review, our objective was to evaluate the safety, immunogenicity, effectiveness, and efficacy of the mpox vaccines. Methods: An extensive search for articles across multiple databases was performed, including searching six databases (PubMed Central, PubMed Medline, Scopus, Web of Science, Cochrane, ProQuest), two pre-print databases (European PMC Preprint and MedRxiv), and Google Scholar. Results: A total of 4290 citations were retrieved from the included databases. Following the removal of duplicates and the initial screening of records, a total of 36 studies were included into the analysis. Additionally, we identified five more studies through manual searches, resulting in a total of 41 eligible articles for qualitative synthesis. The study findings revealed that mpox vaccines demonstrate the ability to generate adequate antibodies; however, their effectiveness may decrease over time, exhibiting varying safety profiles. Most of the included studies consistently reported substantial levels of effectiveness and efficacy against mpox. Interestingly, the number of vaccine doses administered was found to influence the degree of immunogenicity, subsequently impacting the overall effectiveness and efficacy of the vaccines. Furthermore, we found that smallpox vaccines exhibited a form of cross-protection against mpox. Conclusions: Vaccines can be used to prevent mpox and effectively control its spread.


Introduction
Monkeypox virus (MPXV) is a DNA virus in the Poxvirida family, posing a significant threat to public health [1].The World Health Organization (WHO) recognized the escalating monkeypox (mpox) outbreak as a Public Health Emergency of International Concern (PHEIC) on 23 July 2022.MPXV is prevalent in multiple countries across West and Central Africa [2].Since 1 January 2022, WHO has received reports of mpox cases from 111 Member States spanning all six WHO regions.As of 23 May 2023, WHO has recorded a total of 1098 suspected cases and 87,529 laboratory-confirmed cases.These cases have resulted in 141 deaths [3].Fortunately, the International Health Regulations (IHR) Emergency Committee on the multi-country outbreak of mpox held its fifth meeting on 10 May 2023.It concluded that this outbreak is no longer a PHEIC and gave updated interim guidance for a temporary period leading to a long-term mpox control strategy [4].
The MPXV is characterized by two separate lineages; namely, the Western African clade and the Central African clade.In general, the western African strain tends to cause less severe disease compared to the central African strain, with a lower case fatality rate (CFR) of 1-5% versus 10% [5].In the current outbreak, the overall CFR was found to be 8.7%.It was 10.6% (95% CI of 8.4-13.3%)and 3.6% (95% confidence 1.7% to 6.8%) for the central and western African strains, respectively [6].Until recently, sporadic and isolated cases of MPXV outside of the West and Central African regions were primarily linked to individuals who had recently traveled to areas where the MPXV is endemic [7].The WHO Member States that are not considered endemic for virus have also reported cases of mpox.This transmission is concerning as it suggests a potential local transmission or a change in the pattern of MPXV spread [8].Human transmission of infections often occurs through contact with infected animals or other humans.Once infected, large respiratory droplets or contact with a skin lesion can spread the virus from person to person, as well as indirect transmission through contaminated objects (fomites) [9].The incubation period for the virus varies and can range between 7 and 21 days.The duration of the incubation period may be influenced by the nature of the exposure [10].Individuals infected with mpox typically present with a self-limited clinical picture, characterized by a febrile prodrome, lymphadenopathy, and the development of vesicular-popular lesions [11,12].
Children and individuals with immunosuppressive conditions, including Human Immunodeficiency Virus (HIV) infection, are at a higher risk of experiencing severe disease.Encephalitis, secondary cutaneous bacterial infections, sepsis, dehydration, conjunctivitis, keratitis, and pneumonia are all common complications in endemic settings [13][14][15].The secondary attack rate of mpox among unvaccinated household contacts reaches 10%.This means that there is a chance for transmission to occur among individuals who have not received the vaccine and reside in the same household as an infected person [16].
Given the quick global expansion of mpox, the accessibility of potent vaccines, and the ambiguous risk-benefit profile of the available antivirals, vaccination is anticipated to be a key factor in reducing mpox's negative effects on the world [17].It worth noting that the smallpox virus and mpox virus share a significant degree of genetic similarity.Historically, smallpox vaccines have proven to be effective in preventing or reducing the severity of mpox [18].Via T cell epitope mapping, it has been determined that MPXV clade 1 and MPXV-2022 share at least 71% of the vaccinia virus (VACV) T cell epitopes, indicating possible cross-reactivity [19].
By immunizing individuals against mpox, we can reduce the transmission of the virus, mitigate outbreaks, and minimize the severity of the disease [20].At present, mass vaccination for mpox is neither required nor recommended, considering the assessed risks and benefits, regardless of vaccine supply.Post-exposure prophylaxis (PEP) is recommended for individuals who have had contact with mpox cases.In order to avoid the onset of the disease, it entails giving a suitable second-or third-generation vaccination within 4 days of the initial exposure (up to 14 days in the absence of symptoms).Healthcare professionals (HCWs) at high risk of exposure, lab personnel dealing with Orthopoxvirus (OPXV), and clinical laboratory personnel engaged in diagnostic testing for mpox are all advised to use pre-exposure prophylaxis (PrEP) [18].
In 1980, Japanese regulatory authorities granted complete authorization for the liveattenuated vaccination LC16m8 [21].As of 31 August 2007, the ACAM2000 vaccination received authorization from the Food and Drug Administration (FDA) for use in individuals at high risk of contracting smallpox [22].This vaccine contains a replication-competent virus that can spread from the injection site to other parts of the body, and potentially to other individuals.Clinical studies have indicated that myopericarditis occurred at a rate of 5730 cases per million among recipients of ACAM2000.Progressive vaccinia, eczema vaccinatum, visual impairment, blindness, encephalopathy, encephalitis, encephalomyelitis, and other adverse effects have also been associated with this vaccine.Additionally, there have been reports of unvaccinated individuals dying after coming into contact with vaccinated individuals [23,24].According to the Centers for Disease Prevention and Control (CDC) mpox and smallpox vaccines guidance, which was updated on 2 June 2022, a separate vaccine-called JYNNEOS, also known as Imvamune and Imvanex-is currently licensed in the United States of America (USA) for the prevention of smallpox.In 2019, the FDA approved JYNNEOS for smallpox and mpox prevention in adults at high risk of MPXV infection.Unlike ACAM2000, JYNNEOS is a live, non-replicating vaccine based on the Modified Vaccinia Ankara (MVA) strain.It is considered safer for use in immunocompromised individuals as it does not result in live virus production in vaccinated patients [25].Multiple safety studies have been conducted on JYNNEOS.Participants with conditions such as HIV or atopic dermatitis, as well as previously immunized and unimmunized healthy adults, were involved in these studies.The results showed that these individuals did not experience significant adverse events or systemic reactions compared to those who received replicating vaccines [26].In a noteworthy development, on 3 November 2021, the Advisory Committee on Immunization Practices (ACIP) decided to substitute ACAM2000 with JYNNEOS for the immunization of individuals who are at risk of orthopoxviral infection [27].
The variation in the reported vaccine safety and effectiveness could indeed contribute to the high rates of vaccine hesitancy among the general population and HCWs in areas where mpox is endemic [28,29].When there are conflicting or inconsistent reports regarding the safety and effectiveness of vaccines, it can create uncertainty and doubt among individuals considering vaccination [30].
In this review, our objective was to evaluate the safety, immunogenicity, effectiveness, and efficacy of the existing mpox vaccines, including JYNNEOS, ACAM2000, and the live-attenuated LC16m8 vaccines.The findings of this review will offer invaluable insights for healthcare policymakers, enabling them to make well-informed decisions aimed at mitigating the morbidity and financial burden associated with mpox.Additionally, these insights will aid in proactively preventing potential outbreaks in regions where the virus continues to circulate.

Data Source and Search Strategy
The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards were followed in the systematic review.The research team performed an extensive search for articles across multiple databases, including searching 6 databases (PubMed Central, PubMed Medline, Scopus, Web of Science, Cochrane, ProQuest), 2 preprint databases (European PMC Preprint and MedRxiv), and Google Scholar.The search encompassed all available timeframes and had no restrictions on geography or language.The search period extended up to 26 May 2023.The initial search was conducted by two authors, E.E. and A.G., and to ensure the search strategy's accuracy and reliability, RMG independently revised the database search and verified the number of identified citations.The team also cross-checked the citations exported to the reference manager for consistency and completeness.To identify any additional relevant articles, citation tracking was performed by examining the reference list of the identified studies, tracking citations, and exploring related articles.Additionally, a follow-up search of gray literature sources was conducted.For more specific details and a comprehensive overview of the search process, please refer to Supplementary File.

Study Selection and Data Extraction
We included all studies that reported the safety, immunogenicity, effectiveness, or efficacy of mpox vaccines.Our inclusion criteria aimed to cover a wide range of articles, including original studies of various designs, such as randomized control trials (RCTs), nonrandomized control trials, and observational studies.We did not impose any restrictions on the publication date or study design.Furthermore, we considered studies involving individuals of all ages, genders, ethnicities, and geographic locations.Specifically, we focused on studies that investigated both immunizations with smallpox or mpox vaccines and the incidence of mpox.Our exclusion criteria consisted of non-human or in vitro studies, modeling studies, journal articles that were not written in English, conference papers, abstracts, author responses, books, and reviews.We also excluded articles that provided inadequate or overlapping data.All citations were imported into one Endnote library and duplicate citations were removed.Then, the citations were exported to an Excel sheet file for a two-stage screening process: (a) initial title and abstract screening; (b) full-text screening.Any conflicts were resolved by a third expert reviewer (RMG).
Four authors individually screened titles and abstracts (HA, EH, AG, and EE), who excluded non relevant articles.Editorials, reviews, letters, and abstracts only were excluded but screened for potential additional references.Full-text eligibility was conducted by (HA, EH, AG, EE, and MH) and the discrepancies were addressed in study judgments.Four reviewers independently retrieved essential data, extracted from the eligible articles.Data extraction and analysis were performed by (NY, HE, RE, NF, EE, MT) and independently verified by (RMG, MH).

Primary Outcome
To assess mpox vaccines' safety, immunogenicity, efficacy, and effectiveness.

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Secondary attack rate following vaccination and reduction in disease severity in terms of hospitalization and severe symptoms.

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Assess the primary outcomes across the different routes of vaccine administration: intramuscular (IM), intradermal (ID), and subcutaneous (SC) routes.

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Assess the primary outcomes with different numbers of received doses of vaccines: one dose, two doses, and three doses.

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Address the duration of immunological response following vaccination.

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Highlight the effect of different formulations on vaccine immunogenicity.

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Evaluate the cross-reactivity of different vaccines used to prevent other OPXVs from providing protection against mpox.
In the context of the study, several key terms were defined, as follows: (1) Vaccine safety: The assessment of mpox vaccine safety involves the reporting and monitoring of any local or systemic adverse events that occur within 7 days after vaccination or during other specified periods, depending on the specific vaccine being evaluated.(2) Vaccine immunogenicity: Immunogenicity refers to the ability of the mpox vaccine to stimulate an immune response in the individual who receives it.It measures the mpox vaccine's effectiveness in generating an immune reaction, such as the production of antibodies or the activation of specific immune cells, to protect against the target disease.
(3) Vaccine efficacy: Vaccine efficacy is a measure of how well the mpox vaccine prevents the incidence of the disease, typically under controlled and ideal conditions.It is determined through RCTs by comparing the incidence of the disease in a vaccinated group with that in a placebo-controlled group.(4) Vaccine effectiveness: Vaccine effectiveness refers to the performance of the mpox vaccine in real-world conditions, beyond the controlled environment of RCTs.It assesses how well the vaccine performs in preventing the target disease within the general population through observational studies and population-based analyses.

Assessment of the Study Quality
The quality of non-randomized studies was assessed using the Newcastle-Ottawa Scale (NOS).According to the NOS scoring system, studies were classified as follows: Very good studies: scored 9-10 points on the NOS; good studies: scored 7-8 points on the NOS; satisfactory studies: scored 5-6 points on the NOS; unsatisfactory studies: scored 0-4 points on the NOS [31].For non-randomized trials, we used the (ROBINS-E) tool and [32] we used the Cochrane risk of bias tool for the assessment of the quality of RCTs [33] (Supplementary File).

Vaccine Formulations
There are various vaccine formulations available, each with its own unique characteristics and nomenclature.One commonly used vaccine is ACAM2000, which contains live vaccinia virus and is considered a replication-competent smallpox vaccine.ACAM2000 was developed as a successor to the previously used Dryvax vaccine.Dryvax, an attenuated strain of vaccinia virus, was historically utilized for smallpox immunization.ACAM2000 differs from Dryvax in terms of its manufacturing process and production in cell culture rather than in calves.Another notable smallpox vaccine is MVA-BN (Modified vaccinia Ankara-Bavarian Nordic), which is a highly attenuated strain of vaccinia virus.MVA-BN has undergone extensive passaging to achieve further attenuation.This vaccine has been licensed under different names in various countries.In the USA and Europe, it is known as JYNNEOS and Imvamune, respectively.In some countries, it is also marketed as Imvanex.These licensed products of MVA-BN are based on the same strain but may have minor formulation differences or variations in regulatory approval for use in specific regions.

Results
A total of 4290 citations were retrieved for screening.The number of citations obtained from the searched databases were as follows: PubMed Central (n = 460); PubMed Medline (n = 781); Scopus (n = 995); Web of Science (n = 713); Cochrane (n = 10); ProQuest (n = 247); two preprint databases-European PMC Preprint (n = 72) and MedRxiv (n = 32); and Google Scholar (n = 980).We removed 1005 citations as they were found to be duplicates by Endnote.A total of 3285 records were eligible for title and abstract screening; of these, 3072 were excluded (duplicate records (n = 695), irrelevant citations (n = 2377)).After conducting a full-text screening, out of 213 records, 177 studies were irrelevant to the research objective and were consequently excluded.From the remaining 36 studies, an additional 5 were identified through manual searches.Ultimately, 41 articles met the criteria for inclusion and were eligible for qualitative synthesis (Figure 1).
Vaccines 2023, 11, x FOR PEER REVIEW 6 of 32 additional 5 were identified through manual searches.Ultimately, 41 articles met the criteria for inclusion and were eligible for qualitative synthesis (Figure 1).

Smallpox vaccination
The incidence of confirmed case patients was nearly three-times greater in the presumed unvaccinated group than in the presumed vaccinated group, suggesting historical smallpox immunization may have some degree of cross-protection against mpox.

Comparison between pediatric and adult patients and between patients with and without previous smallpox vaccination
Patients under the age of 18 were more likely to be admitted to an intensive care unit.An independent association was found between nausea, vomiting, and mouth sores and a hospital stay lasting more than 48 h and 3 abnormal laboratory tests.No patients passed away, although 5 (15%) were classified as extremely unwell, and 9 (26%) spent more than 48 h in the hospital.Hospitalization or disease severity were not related to previous smallpox immunization.

Smallpox vaccine
The smallpox vaccine does not offer full defense against systemic mpox infection.In both vaccinated and unvaccinated mpox cases, anti-OPXV IgM and CD8 responses predominated, with IgG, CD4, and memory B-cell responses indicating vaccine-derived immunity.Immune indicators showed that some vaccinated people and unvaccinated people had asymptomatic illnesses.The smallpox vaccine does not offer full defense against systemic mpox infection.In both vaccinated and unvaccinated mpox cases, anti-OPXV IgM and CD8 responses predominated, with IgG, CD4, and memory B-cell responses indicating vaccine-derived immunity.Immune indicators showed that some vaccinated people and unvaccinated people had asymptomatic illnesses.

Catala et al. 2022 [68] Spain
To document the clinical and epidemiological characteristics of cases of mpox in the current outbreak.

Smallpox vaccination
Overall, 9% said they had already been immunized against smallpox.All means of administering MVA resulted in the induction of binding antibodies to the whole virus as well as NAbs to the internal mature virion and extracellular enveloped virion forms of the vaccinia virus.These responses were stronger for the higher dose administered via each route.An interferon g enzyme-linked immunospot assay was used to determine the T-cell immunological responses to the vaccine virus, however there was no obvious correlation between the dose or delivery method.

Two doses of MVA Vaccination
Even for those with impaired immune systems, MVA is a safe smallpox vaccine.
There was just one significantly reduced total antibody titer at 2 weeks following the second vaccination, and there were no significant differences between the antibody responses of the uninfected and HIV-infected populations for NAbs.In subjects who had already been exposed to vaccinia, MVA significantly increased the antibody responses, demonstrating its potency against variola.Nine subjects (0.8%) throughout the three lots reported a total of nine serious adverse events (SAEs).Six subjects reported a total of eight cardiac-related adverse events of special interest (AESIs) throughout the entire immunization period (0.5% across the three lots).Nabs antibody GMTs had risen from undetectable two weeks after the second vaccination (at Week 6), to 252.7 for Lot Group 1, 269.9 for Lot Group 2, and 242.0 for Lot Group 3.There were no statistically significant differences between the three lot groups for neutralizing and total antibodies; however, seroconversion rates 2 weeks after the second vaccination were above 98.0% for both Nabs and total antibodies in all groups.

The Overall Mpox Vaccines Efficacy and Effectiveness
Almost all of the studies reported positive findings of the vaccination against mpox, with the exception of five studies.Cohn et al. [70] discovered that recombinant mpox proteins and native proteins barely bound to the JYNNEOS vaccina sera.Furthermore, vaccination with JYNNEOS does not stimulate a significant B cell response.In comparison to the vaccination, recent mpox infection (within 20-102 days) produced strong serum antibody responses to A29L, A35R, A33R, B18R, and A30L, as well as to native mpox proteins.However, those who received the JYNNEOS vaccine displayed CD4 and CD8 T cell responses against orthopox peptides that were equivalent to those seen following mpox infection.Similarly, Zaeck et al. [56] found that in non-primed people, the two-shot MVA-BN immunization series results in comparatively low levels of MPXV-neutralizing antibodies (Nabs).Karem et al. [37] concluded that systemic mpox infection is not fully protected against smallpox immunization.Catala et al. [68] revealed that there was no difference in the extension or number of lesions between patients who had received a smallpox vaccination or not in terms of the risk factors for severity.One dose of MVA-BN for PEP was ineffective in preventing symptomatic mpox in 10% of vaccinated people.The clinical illness appeared within 21 days of exposure, even with PEP, with contact with an mpox case [60].

Immunogenicity
Seven studies addressed the immunogenicity of different mpox vaccines.Protection was associated with the prior induction of Nabs to MVA or vaccinia virus [40].Clinical and virologic protection against the Dryvax challenge is achieved through MVA immunization.Similarly, LC16m8 generates Nabs antibody titers to multiple poxviruses, including vaccinia, mpox, and variola major, and broad T-cell responses [42].92% of IMVANEX recipients and 97% of MVA-HIV recipients had anti-MVA antibodies up to 12 weeks after the illness started [61].Based on vaccines against the vaccinia virus (VACV), it was expected that the cellular immunity induced by these vaccinations against MPXV-2022 would resemble that observed for the first-generation vaccines against MPXV-CB (Congo Basin lineage) [59].In comparison to natural infection, patients who received the JYNNEOS vaccine showed equivalent CD4 and CD8 T cell responses to orthopox peptides.However, JYNNEOS immunization does not elicit a robust B cell response [70].Sammartino et al. [64] found that, in naïve subjects, a second dose boosts the serological response to levels similar to those of the MPXV infected patients.Of note, the production of antibodies differed across ages: NAbs titer of 1/20 or more in 33.3 to 53.2% of people older than 45 years.Among people 30-45 years old who probably have not been vaccinated, the proportion with virus NAbs ranged between 3.2 and 6.7% [66].

Safety and Adverse Events
Safety and adverse effect were reported in five studies.Kennedy et al. [42].reported that the local and systemic effects following LC16m8 immunization were comparable to those described with Dryvax.For either vaccine, there were no clinically significant abnormalities suggestive of heart damage.Greenberg et al. [43] found that MVA is a safe smallpox vaccine, even for immunocompromised individuals.The third study conducted by Duffy [44] during the 2022 mpox outbreak, found that monitoring of the JYNNEOS vaccine's safety in the USA did not reveal any fresh or unanticipated safety issues among adults.Sharff et al. [49] reported 10 cardiac Adverse Events of Special Interest (AESI) out of 3236 doses following JYNNEOS vaccination, with an incidence of 3.1 per 1000 doses.Regarding local solicited adverse events (AEs), 91.2% of all participants experienced these adverse events after the formulation of MVA-BN by.The most common local solicited AEs were injection site pain and injection site erythema.During the entire immunization period, 69.6% of all individuals reported experiencing general solicited adverse events.Myalgia, tiredness, and headache were the most often reported general requested AEs.Nine subjects (0.8%) reported a total of nine serious adverse events (SAEs).Six individuals reported a total of eight cardiac-related adverse events of special relevance over the entire immunization period [26].

Vaccine Efficacy and Effectiveness
Regarding vaccine efficacy, Whitehouse et al. [62] described the incidence of confirmed mpox as being almost three-times higher among those presumed unvaccinated than among those presumed vaccinated.Arbel et al. [54] found that 3 vaccinated individuals did not have MPXV infection, but 15 unvaccinated people did (40.0 per 100,000 person-days) (6.4 per 100,000 person-days) 79% (95% CI: 24-94%).A 79% decrease in the likelihood of infection was found in those who are susceptible to MPXV infection.According to Rimoin et al. [51], the vaccine's effectiveness was estimated to be 80.7% (95% confidence interval: 68.2-88.4%).
Few studies assessed the secondary attack rate and risk of hospitalization.The secondary attack rates among unvaccinated and vaccinated contacts were 0.017 and 0.004, respectively [50].Immunizations resulted in decreased hospitalization rates (2%) compared to unvaccinated patients (8%).Vaccinations also reduce the incidence of systemic symptoms such as fever and chills [45].

Route of Administration Intradermal, Intramuscular, Subcutaneous
MVA-delivered intradermal (ID) exhibits immune and protective responses comparable to those of a 10-fold greater dosage administered subcutaneously (SC) [40].Furthermore, ID immunization with MVA elicits similar antibodies to those elicited by the IM or SC routes but at a 10-fold-lower dose [41].Frey et al. [38] found that there were no significant differences between IM or SC routes for IMVAMUNE, except for in induration.It was found that all routes of MVA produced binding antibodies to the whole virus, as well as NAbs to the internal mature virion and extracellular enveloped virion forms of the vaccinia virus [41].

Single Dose
Many studies assessed the protective effect of one dose of mpox vaccination.In the high-risk population, a single dosage of SC MVA-BN is connected to a significantly reduced probability of MPXV infection [55].Of 10,068 individuals who received the first dose of the MVA-BN vaccination, 15 (0.15%) developed mpox subsequently.All of the identified individuals were gay and bisexual men (GBM), with 12/15 (80%) on PrEP and 3/15 (20%) being People Living With HIV (PLWH) [59].Furthermore, a single SC MVA-BN dose is associated with a considerably reduced probability of MPXV infection in the high-risk cohort [58].It was discovered that a dose of the JYNNEOS vaccine can decrease the severity of mpox disease in people who contract it after receiving the vaccine.Some symptoms were reported less frequently among vaccinated than unvaccinated mpox patients.Gushchin et al. [66] studied the optimal duration following the first dose of vaccination to provide protection against MPXV infection.Within two weeks of receiving the first dose of MVA-BN, the majority of postvaccination mpox infections occurred before complete efficacy was expected to have been reached.

One Dose versus Two Doses
T cell responses were retorted after two MVA doses.The MVA immunization boosts the safety and immunogenicity of subsequent Dryvax ® vaccinations.It was both safe and immunogenic [39].The immunogenic response among immunocompromised patients was addressed by Greenberg et al. [43].The antibody responses of the HIV-positive and uninfected populations to NAbs did not differ significantly.There was only one significantly decreased total antibody titer at two weeks after the second dose of vaccination.Following immunization, MVA dramatically boosted the antibody responses in the subjects.

Third Dose
A third vaccination with the same MVA-based vaccine considerably increases the antibody response, but dose-sparing of an MVA-based influenza vaccine results in reduced MPXV-Nabs levels [56].After the MVA-MERS-S vaccine, only one participant experienced cross-reactive mpox virus NAbs; following the second dose, three out of ten and the third dose, ten out of ten, respectively, experienced this reaction.On the other hand, Frey et al. [38] reported for the IMVAMUNE vaccination, a dose-response was visible for the first and second doses, but not for the third.

Duration of Serological Response
The duration following vaccination was important to determine the immunogenic response; two weeks following the second vaccination, the Nabs Geometric Mean Titers (GMTs) had increased significantly.For both Nabs and total antibodies, the seroconversion rates were higher than 98.0% in all groups two weeks after the second vaccination [26].Previously naïve and vaccinated participants generated vaccinia virus and MPXV-NAbs in response to the JYNNEOS vaccination.Most participants remained IgG seropositive at the 2-year timepoint.Similarly, Priyamvada et al. [53] found that the antibody titers were strongly boosted by vaccination (peak at D42) but declined to baseline levels two years post-vaccine.Falvi et al. [69] discovered that although MVA-specific NAb IgG titers decreased over the course of five months following the second vaccination, they remained above baseline.

Formulation
Compare the stability, immunogenicity, and safety of the normal MVA formulation, dosage, and mode of administration with those of a more stable, lyophilized formulation and an intradermal ID route that spares antigens.Only after the initial vaccination did moderate/severe functional, local reactions substantially differ between the lyophilized-SC (30.3%), liquid-SC (13.8%), and liquid-ID (22.0%) groups.After receiving any vaccination, the Liquid-SC group (58.1%), the Lyophilized-SC group (58.2%), and the Liquid-ID group all experienced moderate-to-severe quantifiable erythema and/or induration (58.1%).In addition, 36.1% of the participants in the ID group experienced temporary, minor skin darkening at the injection site.The GMTs of the peak NAbs titers for the Lyophilized-SC, Liquid-SC, and Liquid-ID groups, respectively, were 87.8, 49.5, and 59.5 after the second vaccination day , and the maximum proportion of responders based on peak titer in each group was 97.9%, 95.3%, and 194.5%, respectively.Only 54.3%, 39.2%, and 35.2% of individuals were still seropositive for the lyophilized-SC, liquid-SC, and liquid-ID groups 180 days after the second vaccination, when the geometric mean NAbs dropped to 11.7, 10.2, and 10.4, respectively [71].

Cross-Reactivity
Ten studied focused on the cross-reactivity of pervious small pox vaccination on acquiring mpox.Ilchmann et al. [35] found that NAbs geometric mean titers increased after vaccination among naïve participants and among those who received a prior smallpox vaccination.Kennedy et al. [42] found that LC16m8 generates Nabs antibody titers to multiple poxviruses, including vaccinia, mpox, and variola major, as well as broad T-cell responses.Zeng et al. [63] found that only 26.7% of the sera collected from individuals born ≤1981 were positive using the MPXV IgG Elisa kit, which is consistent with MPXV Nabs.Rimoin et al. [51] reported that the risk of human mpox is inversely associated with smallpox vaccination.Similarly, Sharff et al. [49] found that smallpox vaccination may confer cross-protection to mpox; 8.5% of the vaccinated subjects had detectable antibodies against mpox.Thornhill et al. [34] found that among 528 MPXV-infected patients, 9% had received the smallpox vaccination.The vaccine effectiveness of the prior first-generation smallpox vaccine against more severe mpox was 58% [57].However, Huhn et al. [36] highlighted that previous smallpox vaccination was not associated with disease severity or hospitalization.
According to Fine et al. [50], immunization offered a high level of protection to the 70% of contacts who had already received vaccinations.A degree of cross-protection against mpox may be granted by historical vaccination against smallpox.Jezek et al. [52] reported that the second attack rate for contacts without a vaccination scar (7.2%) was significantly different from the attack rate for individuals who had previously had a vaccination (0.9%).

Discussion
In this review, our goal was to provide a clear understanding of the safety, immunogenicity, efficacy, and effectiveness of various mpox vaccines.In addition, we aimed to determine the second attack rate following vaccination, disease severity, and hospitalization following vaccination and assess the primary outcomes across different routes of vaccination, and the number of doses received.Finally, we highlighted the cross-reactivity of different vaccines against mpox and the duration of the immunological response, with a special focus on vaccine formulation.We analyzed a total of 41 studies to gather the relevant information.It is important to note that immune responses to one OPXV can also recognize other OPXV.The level of protection provided may vary depending on the similarity between the OPXV.With the eradication of smallpox and the subsequent discontinuation of smallpox immunization, there has been a significant rise in mpox cases.This can be attributed to several factors.Firstly, the growing population consists of individuals with limited immunological experience because of the absence of smallpox and the discontinuation of vaccination since 1980.Additionally, the increase in the number of newly infected individuals can be attributed to genetic variations within the pathogen itself and the substantial influx of travelers.Furthermore, increased human exposure to animals has occurred due to deforestation, population migration, and armed conflicts [14,73,74].

Vaccine Efficacy Is Variable Based on the Vaccine Type
Previous studies have demonstrated that the severe complications and sequelae associated with mpox are more common in unvaccinated than in vaccinated patients [11].Participants who had no prior history of smallpox vaccination or exposure had lower baseline antibody levels but saw a comparable fold-rise in anti-body titers by day 42 as those who had a prior history of immunization.In response to JYNNEOS immunization, both previously unvaccinated and vaccinated subjects produce vaccinia virus and MPXV-Nabs.Finally, even while the overall mpox-specific IgG titers and Nabs titers fell from their peak and rebounded to near baseline levels by the 2-year mark, the majority of patients remained IgG seropositive [53].Smallpox and mpox vaccinations can be administered before exposure to prevent infection and disease, or after exposure to treat infection and disease.Pre-exposure immunization is recommended to protect the most vulnerable people.This level of protection is best achieved with a second-or third-generation vaccination.Post-exposure immunization should be delivered after 4 days of exposure to prevent illness, but it can be used up to 14 days later to reduce disease severity.Post-exposure vaccination is likewise most effective with a second-or third-generation vaccine [75].Among the first 1000 mpox cases in the Netherlands, the prior first-generation smallpox vaccine had 58% (95% CI 17-78%) effectiveness against more severe mpox symptoms, implying moderate protection against more severe mpox symptoms in addition to any possible protection against mpox infection and disease [57].10% of vaccinated contacts of mpox cases did not experience symptomatic mpox immunity following a single MVA-BN dose of PEPV.The symptomatic disease developed after contact with a mpox case within 21 days after exposure.This highlighted the value of the avoidance of exposure to MPXV as the vaccination does not provide 100% protection when given either pre-or post-exposure.

Efficacy and Effectiveness of Monkeypox Vaccines
It has been demonstrated that a single immunization dose protects against MPXV and lessens the severity of symptoms.Before full efficacy was likely, the bulk of postvaccination mpox infections happened within two weeks [55].Some cases that arose between 1 and 14 days after vaccination may not represent true vaccine failure because the people involved sought immunization after realizing that they had been exposed because the incubation period for mpox is 7 to 21 days.After the second vaccination dosage, the protection was more noticeable.A third dose was permitted to boost protection.
During mpox vaccine trials, one potentially confusing situation arose.A few reports of outbreaks of mpox, particularly in Africa, have noted diagnostic confusion with chickenpox, another viral disease (varicella).The appearance of the exanthems might be extremely similar.On occasion, a population has been infected by two viral infections simultaneously.If a patient was exposed to mpox and received the immunization but developed a rash afterward, they would be considered vaccine failures.However, even if the rash had been misidentified as chickenpox, the mpox immunization would still have been successful [76].

Vaccine Safety
When compared to other replication-competent vaccinia-based smallpox vaccines, MVA-BN offers an improved safety profile as it has been attenuated to the point where it cannot replicate in mammals.Other live vaccines, including ACAM2000, have been associated with increased rates of acute myo-/pericarditis (1:200) and adverse effects relating to the heart, like dyspnea at rest (1:100) [24,77,78].The MVA-BN vaccine thereby addresses a number of safety issues that have restricted the use of earlier versions of smallpox immunizations.No significant AEs linked to the vaccine support MVA-outstanding BN's safety record.In stark contrast to what has been observed with replicating smallpox immunizations, Overton et al. [26] discovered that no cardiac inflammatory problems were recorded in any participant who had received the MVA-BN vaccination [24,27,77,78].Similar to other MVA-BN investigations, local and general responses that were typically mild to moderate in intensity and self-limiting were the most often reported adverse effects following the administration of FDMVA-BN.The incidence has significantly dropped, which may be due to a number of factors, such as behavioral modifications and a gain in immunity among the susceptible population, either acquired spontaneously or as a result of targeted vaccination programs.

Limitations and Strengths
This study represents one of the pioneering efforts in examining the safety profile, immunogenicity, efficacy, and effectiveness of mpox vaccines.It sheds light on an important aspect of research that has been relatively scarce in the literature.A key strength of this review is the comprehensive inclusion of a large number of literature sources.The review not only encompassed published studies available in databases, but also unpublished data, such as preprints.The review included a substantial number of studies, with a total of 41 studies being selected for analysis.These studies collectively encompassed a significant participant pool.Furthermore, to ensure the integrity of the study and to minimize bias, we adhered to specific inclusion and exclusion criteria during the study selection process.However, more information about the brand name of the smallpox vaccine that was used could not be added as it was not available in the included studies.Finally, we assessed the quality of the included studies based on the study type, as recommended by the PRISMA guidelines.

Conclusions
Mpox is a growing health problem; however, there is a scarcity of studies that assess the vaccines' safety profile, immunogenicity, safety, and efficacy.Mpox vaccines can be used to effectively prevent the disease and control its further spread.Cross-reactivity induced by smallpox vaccines provides sufficient immunity against mpox.In many studies, mpox resulted in the development of an immunological response similar to that developed by natural infection.However, there is an urgent need to conduct more research focusing on racial response differences and responses among high-risk populations to ensure the health emergency preparedness to combat this disease.

Supplementary Materials:
The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/vaccines11111708/s1,Table S1: Database Search.Funding: There has been no financial support for this work that could have influenced its outcome.

Institutional Review Board Statement:
No ethical approval is needed as systematic reviewing is based on published trial results.

Figure 1 .
Figure 1.PRISMA 2020 flow diagram for updated systematic reviews which included searches of databases and registers only.

Figure 1 .
Figure 1.PRISMA 2020 flow diagram for updated systematic reviews which included searches of databases and registers only.
PCR-based molecular assays were used for the diagnosis of mpox.Exclusion: 1. Cases without fever or rash 2. Cases with negative PCR Smallpox vaccine Inversely correlated with smallpox immunization is the risk of human mpox.The predicted vaccine effectiveness was 80.7% (95% CI: 68.2-88.4%).
mpox virus-infected patients with skin/dermatological lesions Regarding risk factors for severity, the study found no distinction in the extension or quantity of lesions between patients who had received a smallpox vaccination or not.Thornhill et al. 2022[34], multi-national study Describe the presentation, clinical course, and outcomes of PCR-confirmed monkeypox virus infections.

Author
Contributions: R.M.G.Conceptualization of the research idea, built the search strategy, screened the included citations, shared in data extraction, and wrote and reviewed the manuscript.N.F.assessed the quality and data extracted.E.H.E.wrote the manuscript, assessed the quality, and data extracted.M.M.T. screened articles and data extracted.A.G. Research strategy, database search, screened articles, data extracted, and Prisma, and.E.E.M.H. screened articles and data extraction.N.Y.assessed the quality and data extracted.H.A. screened articles and data extracted.E.E.database searched and data extracted.R.E., E.E.M.H., and E.M.H. completed data extraction.M.H. wrote the manuscript, database searched, screened the included citations, assessed the quality, critically revised the manuscript, submitted it, and responded to reviewers' comments.E.E.M.H., Z.E.E.M., A.S.A.Z., R.A.A.A., E.A.S.S., A.S.A. and A.F.A. critically revised the manuscript.All authors have read and agreed to the published version of the manuscript.

Table 1 .
Shows the characteristics of included studies.