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Vaccines
Special Issues
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: 28 February 2026 | Viewed by 4343

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 100 words) can be sent to the Editorial Office for announcement on this website.

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 (3 papers)

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Research

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
Viewed by 281
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 1119
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 2466
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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