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Vaccines
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The Effectiveness of Influenza Vaccine
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The Effectiveness of Influenza Vaccine

A special issue of Vaccines (ISSN 2076-393X). This special issue belongs to the section "Influenza Virus Vaccines".

Deadline for manuscript submissions: 31 August 2026 | Viewed by 14159

Special Issue Editors

Dr. Filippo Ansaldi

E-Mail Website
Guest Editor
Department of Health Sciences, University of Genoa, 16126 Genoa, Italy
Interests: candidiasis
Special Issues, Collections and Topics in MDPI journals
Dr. Amicizia Daniela

E-Mail Website
Guest Editor
Department of Health Sciences, University of Genoa, 16132 Genoa, Italy
Interests: vaccines; influenza; healthcare planning; HTA; health promotion
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Influenza vaccines reduce the disease burden by lowering the risk of infection, severe illness, and complications. Their effectiveness can vary each year due to several factors, including changes in the virus, the selection of vaccine strains, age groups, and individual immune responses. Ongoing research aims to improve vaccine formulations and develop influenza vaccines that offer more robust and longer-lasting protection. Research is also critical for evidence-based decision-making in public health and is fundamental to maintaining progress and trust in immunization programs. This Special Issue will address all aspects of influenza vaccine effectiveness.

Dr. Filippo Ansaldi
Dr. Amicizia Daniela
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Vaccines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • effectiveness
  • influenza vaccines
  • infection control
  • influenza vaccination
  • seasonal influenza vaccines

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Published Papers (6 papers)

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14 pages, 405 KB  
Article
Primary Care-Based Estimates of Influenza Vaccine Effectiveness in Hungary, 2024/25
by Gergő Túri, Viktória Velkey, Krisztina Mucsányiné Juhász, Katalin Krisztalovics, Annamária Ferenczi, Csaba Luca, Edit Bilics, Katalin Kristóf and Beatrix Oroszi
Vaccines 2026, 14(4), 342; https://doi.org/10.3390/vaccines14040342 - 13 Apr 2026
Viewed by 551
Abstract
Background: The 2024/25 influenza season in Hungary experienced a major surge in cases, the largest since the COVID-19 pandemic. We evaluated influenza vaccine effectiveness (VE) in primary care settings among adults and vaccination target groups, and also according to time since vaccination, prior [...] Read more.
Background: The 2024/25 influenza season in Hungary experienced a major surge in cases, the largest since the COVID-19 pandemic. We evaluated influenza vaccine effectiveness (VE) in primary care settings among adults and vaccination target groups, and also according to time since vaccination, prior seasonal vaccination, and influenza type. Methods: A test-negative case–control study was conducted in Hungary. Data and specimens were collected from primary care patients with an acute respiratory infection (ARI). Patients with positive PCR test results for influenza were classified as cases, while those with negative test results for influenza were classified as controls. Adjusted VEs were calculated using logistic regression as (1 − odds ratio of vaccination) × 100. Results: Between November 2024 and May 2025, 2074 patients were included in the analysis, of whom 395 cases had influenza. Of the 129 vaccinated patients, 123 (95%) received trivalent inactivated adjuvanted whole-cell vaccine (TIAV), and 6 (5%) received quadrivalent split-virion vaccine. The VE against any influenza was 53% (95% CI: 13–74) in the 18+ age group and 52% (95% CI: 7–75) in the target group for vaccination. The VE against any influenza was 63% (95% CI: 17–84) 14–89 days after vaccination, and 27% (95% CI: −67–68) 90 days or more after vaccination. The VE against any influenza was 56% (95% CI: 1–80) with both current and prior seasonal vaccination, and 5% (95% CI: −64–45) with only prior seasonal vaccination. The VE against influenza A was 39% (95% CI: −16–68), and against influenza B was 80% (95% CI: 2–96). Conclusions: We observed moderate vaccine effectiveness against any influenza, with higher protection within three months after vaccination. Our research findings provide evidence to inform the development of vaccines and the scheduling of vaccination campaigns, with the aim of maximizing the level of protection provided by vaccines throughout the entire influenza season. Full article
(This article belongs to the Special Issue The Effectiveness of Influenza Vaccine)
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11 pages, 218 KB  
Article
Impact of the 2023/24 Influenza Vaccination on Patients with Inflammatory Rheumatic Disease in Germany: Insights from a Nationwide, Longitudinal, Self-Reported Study
by Karolina Gente, Benedikt Ditz, Eike Bormann, Nadine Al-Azem, Gerd R. Burmester, Salma Charaf, Christian Fräbel, Gabriele Gilliam-Feld, Natalie Klüser, Anna Knothe, Ulf Müller-Ladner, Johannes Roth, Hendrik Schulze-Koops, Christof Specker, Mirko Steinmüller, Konstantinos Triantafyllias and Rebecca Hasseli
Vaccines 2026, 14(2), 136; https://doi.org/10.3390/vaccines14020136 - 29 Jan 2026
Viewed by 1167
Abstract
Background: Patients with inflammatory rheumatic diseases (IRD) are susceptible to influenza infections and their complications. However, they may avoid vaccination for fear of exacerbating their IRD. This study evaluates the 2023/24 influenza vaccine in IRD patients, aiming to provide recommendations for this group [...] Read more.
Background: Patients with inflammatory rheumatic diseases (IRD) are susceptible to influenza infections and their complications. However, they may avoid vaccination for fear of exacerbating their IRD. This study evaluates the 2023/24 influenza vaccine in IRD patients, aiming to provide recommendations for this group in the upcoming season. Methods: In this prospective, longitudinal study, we assessed the self-reported impact of influenza vaccination on patients with IRD. Participants were recruited nationwide between October and December 2023 and completed an online questionnaire after vaccination as well as at three and six months of follow-up. Results: Among 633 patients, 87.5% were female, with a median age of 50.4 (18–84) years. Post-vaccination, 50% experienced injection site pain; 41% reported no side effects. IRD flares occurred in 5%, with 1% requiring changes to immunomodulation. Among 428 patients with follow-up, influenza infections were reported in 38 patients (8.9%), including 10 (2.3%) with reinfections. No severe cases requiring hospitalization were reported. Spondyloarthritis patients had higher susceptibility to influenza (p = 0.002), accounting for 55.3% of infections. IRD flare-ups in the 12 months before vaccination predicted infections (p = 0.002). Conclusions: The 2023/24 vaccine was well tolerated by IRD patients, with no impact on the course of the disease in 95% of cases. Only 9% of patients reported influenza infections, none of which were severe. In light of these findings, physicians are advised to recommend vaccination to eligible IRD patients prior to or in the respective season. Full article
(This article belongs to the Special Issue The Effectiveness of Influenza Vaccine)
17 pages, 3793 KB  
Article
Genetic Divergence of H1N1pdm09 in Saudi Arabia: Unveiling a Novel N-Glycosylation Site and Its Role in Vaccine Mismatch
by Shatha Ata Abdulgader, Abdulhadi M. Abdulwahed, Abdulaziz M. Almuqrin, Ibrahim M. Aziz, Noorah A. Alkubaisi, Reem M. Aljowaie, Mohamed A. Farrag, Abdulkarim F. Alhetheel, Adel A. Abdulmanea, Fatimah N. Alanazi, Asma N. Alsaleh and Fahad N. Almajhdi
Vaccines 2025, 13(11), 1111; https://doi.org/10.3390/vaccines13111111 - 30 Oct 2025
Cited by 2 | Viewed by 1393
Abstract
Background/Objectives: Influenza A virus undergoes continuous antigenic drift, necessitating annual vaccine reformulation. Saudi Arabia faces unique epidemiological challenges owing to mass gatherings during religious pilgrimages and the dynamic movement of foreign workers. This study aimed to characterize the genetic diversity of hemagglutinin ( [...] Read more.
Background/Objectives: Influenza A virus undergoes continuous antigenic drift, necessitating annual vaccine reformulation. Saudi Arabia faces unique epidemiological challenges owing to mass gatherings during religious pilgrimages and the dynamic movement of foreign workers. This study aimed to characterize the genetic diversity of hemagglutinin (HA) and neuraminidase (NA) genes of influenza A viruses circulating in Riyadh and to assess their match with vaccine strains during the 2024–2025 period. Methods: Nasopharyngeal samples (n = 363) were collected from patients presenting with influenza-like illness. RT-PCR was used for detection and subtyping. Sequence and phylogenetic analysis of the complete HA and NA gene sequences from A/H1N1pdm09 strains (n = 7) were then performed. Results: Of the 363 samples, 110 (30.3%) were positive for influenza A; among these, 68 (61.8%) were A/H1N1pdm09, and 42 (38.2%) were H3N2. Phylogenetic analysis revealed that all A/H1N1pdm09 strains belonged to clade 5a.1, distinct from vaccine strains. In comparison with the vaccine strain A/Wisconsin/67/2022, seven amino acid substitutions in the HA gene and eight in the NA gene were recorded in Saudi circulating strains. The significant genetic divergence between circulating A/H1N1pdm09 strains and current vaccine strains indicates potential vaccine mismatch. Conclusions: The significant genetic divergence between circulating A/H1N1pdm09 strains and current vaccine strains suggests potential vaccine mismatch. Continuous surveillance programs along with vaccination plans are necessary to tackle the changing influenza A virus strains in the special epidemiological context of Saudi Arabia. Full article
(This article belongs to the Special Issue The Effectiveness of Influenza Vaccine)
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15 pages, 852 KB  
Article
Effect of Influenza Vaccination on the Disease Severity and Viral Load Among Adult Outpatients and Inpatients
by Alexander Domnich, Vincenzo Paolozzi, Giada Garzillo, Andrea Orsi and Giancarlo Icardi
Vaccines 2025, 13(10), 1046; https://doi.org/10.3390/vaccines13101046 - 10 Oct 2025
Viewed by 5279
Abstract
Background: Some studies suggest that, thanks to the mechanisms of immune-mediated attenuation, influenza vaccination reduces severity of influenza illness in breakthrough infections. This study aimed to assess whether influenza vaccination attenuates severity of laboratory-confirmed influenza among Italian adults. Methods: This secondary [...] Read more.
Background: Some studies suggest that, thanks to the mechanisms of immune-mediated attenuation, influenza vaccination reduces severity of influenza illness in breakthrough infections. This study aimed to assess whether influenza vaccination attenuates severity of laboratory-confirmed influenza among Italian adults. Methods: This secondary analysis included all influenza cases detected during respiratory surveillance studies conducted in outpatient and inpatient settings in Genoa (Italy), throughout the 2023/2024 and 2024/2025 seasons. Here, we compared viral load and the count of influenza-related symptoms in outpatients, alongside all-cause in-hospital mortality and radiologically confirmed pneumonia in inpatients, between vaccinated and unvaccinated adults. Results: The study included 188 influenza cases diagnosed in primary care and 281 influenza cases identified among inpatients. Of these, 37.2% and 31.7%, respectively, were vaccinated, constituting breakthrough infections. Compared to unvaccinated adults, vaccinated outpatients had a slightly lower viral load (difference in cycle threshold values of 1.36 corresponding to about 0.51 log10 reduction in the number of copies/mL; p = 0.077), primarily driven by influenza A(H1N1)pdm09. Vaccinated outpatients also reported 9% fewer influenza-related symptoms than unvaccinated counterparts [prevalence ratio 0.91; 95% confidence interval (CI): 0.84, 0.99]. Among hospitalized older adults, influenza vaccination was associated with 64% reduced odds of in-hospital death (odds ratio 0.36; 95% CI: 0.12, 0.94). Conversely, no association between vaccination and development of pneumonia was found. Conclusions: This study corroborates the idea that influenza vaccination attenuates disease severity in breakthrough infections. These effects are, however, dependent on the measure of severity used. Full article
(This article belongs to the Special Issue The Effectiveness of Influenza Vaccine)
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14 pages, 1731 KB  
Article
COVID-19 Vaccination Enhances the Immunogenicity of Seasonal Influenza Vaccination in the Elderly
by Engin Berber, Fani Pantouli, Hannah B. Hanley and Ted M. Ross
Vaccines 2025, 13(5), 531; https://doi.org/10.3390/vaccines13050531 - 16 May 2025
Cited by 1 | Viewed by 3710
Abstract
Background/Objectives: The co-circulation of both influenza viruses and SARS-CoV-2 poses a significant health risk, especially for the elderly. While vaccination against both diseases remains an effective strategy to reduce the burden of symptomatic infections, the effect of administering COVID-19 mRNA and seasonal influenza [...] Read more.
Background/Objectives: The co-circulation of both influenza viruses and SARS-CoV-2 poses a significant health risk, especially for the elderly. While vaccination against both diseases remains an effective strategy to reduce the burden of symptomatic infections, the effect of administering COVID-19 mRNA and seasonal influenza vaccines (COV-Flu) on elicited antibody responses has not been explored. Methods: Participants between 18 and 90 years old were vaccinated with COVID-19 mRNA vaccines (n = 67), seasonal influenza vaccines (n = 130), or both (n = 201) within a three-month period between 2021 and 2024. Serum hemagglutination-inhibition (HAI) titers against influenza A (H1N1, H3N2) and B (Yamagata, Victoria) strains were measured from the COV-Flu participants or the participants vaccinated with influenza vaccines only (mono-Flu). SARS-CoV-2 neutralization assays were performed on sera collected from the COV-Flu participants and the participants receiving the mRNA vaccine only (mono-COVID-19). Results: The administration of influenza virus vaccines and COVID-19 mRNA vaccines within a three-month period significantly enhanced the post-vaccination HAI titers against both influenza A and B vaccine components, particularly in the elderly (65–90) participants. There were no significant differences in SARS-CoV-2 neutralization titers in COV-Flu participants compared to mono-COVID-19 participants. Conclusions: Vaccination with both the COVID-19 mRNA and influenza vaccines enhances influenza-specific HAI titers without compromising the neutralization titers elicited by COVID-19 mRNA vaccination against SARS-CoV-2, especially in the elderly. These findings indicate the potential benefits of this approach, particularly for older adults, by boosting influenza virus vaccine-induced serum HAI activity while maintaining COVID-19 protective immunity. Full article
(This article belongs to the Special Issue The Effectiveness of Influenza Vaccine)
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14 pages, 1334 KB  
Systematic Review
Influenza Vaccine Effectiveness in Korea: A Systematic Review and Meta-Analysis of Real-World Evidence from the Past Decade
by Hye Su Jeong and Hye Young Kim
Vaccines 2026, 14(3), 217; https://doi.org/10.3390/vaccines14030217 - 27 Feb 2026
Viewed by 1139
Abstract
Background: Influenza remains a significant public health burden. Although vaccination is the most effective preventive strategy, evidence on influenza vaccine effectiveness (VE) in Korea remains fragmented. Methods: A systematic review and meta-analysis were conducted on real-world Korean influenza VE studies published from January [...] Read more.
Background: Influenza remains a significant public health burden. Although vaccination is the most effective preventive strategy, evidence on influenza vaccine effectiveness (VE) in Korea remains fragmented. Methods: A systematic review and meta-analysis were conducted on real-world Korean influenza VE studies published from January 2016 to October 2025. Literature research was performed in PubMed, Embase, and Web of Science. Eligible studies evaluated influenza VE using real-world data sources. Pooled VE estimates were calculated using a random-effects model and stratified by age group and virus type. Results: A total of 2922 records were identified, of which nine studies met the inclusion criteria and eight were included in the meta-analysis. Eight of nine studies were conducted in hospital settings. Five studies targeted adults (including two focusing on those aged ≥ 65 years), and four targeted children. Six of the nine studies evaluated single influenza seasons, while the remaining three covered multiple seasons. Statistically significant VE was observed among adults (23.6%, 95% confidence interval [CI]: 13.8 to 32.2), children (25.2%, 95% CI: 8.2 to 39.0) and against influenza A in children (32.4%, 95% CI: 17.7 to 44.4). Conclusions: This study synthesized a decade of fragmented VE evidence in Korea. Findings suggest suboptimal effectiveness compared to global estimates, highlighting the need for further evaluation of alternative vaccine platforms, including cell-based vaccines, within Korea’s national immunization strategy. Full article
(This article belongs to the Special Issue The Effectiveness of Influenza Vaccine)
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