Abstract
Vaccination could be an evolutionary pressure on seasonal influenza if vaccines reduce the transmission rates of some (“targeted”) strains more than others. In theory, more vaccinated populations should have a lower prevalence of targeted strains compared to less vaccinated populations. We tested for vaccine-induced selection in influenza by comparing strain frequencies between more and less vaccinated human populations. We defined strains in three ways: first as influenza types and subtypes, next as lineages of type B, and finally as clades of influenza A/H3N2. We detected spatial differences partially consistent with vaccine use in the frequencies of subtypes and types and between the lineages of influenza B, suggesting that vaccines do not select strongly among all these phylogenetic groups at regional scales. We did detect a significantly greater frequency of an H3N2 clade with known vaccine escape mutations in more vaccinated countries during the 2014–2015 season, which is consistent with vaccine-driven selection within the H3N2 subtype. Overall, we find more support for vaccine-driven selection when large differences in vaccine effectiveness suggest a strong effect size. Variation in surveillance practices across countries could obscure signals of selection, especially when strain-specific differences in vaccine effectiveness are small. Further examination of the influenza vaccine’s evolutionary effects would benefit from improvements in epidemiological surveillance and reporting.
Highlights
Vaccination against seasonal influenza is intended to reduce the incidence of disease
At the type and subtype level, test-negative design (TND) studies from the 2009–2010 to the 2016–2017 seasons suggest that the vaccine has been less effective against H3N2 than against B or H1N1
We find that H3N2 is relatively less common than B in the more vaccinated
Summary
Vaccination against seasonal influenza is intended to reduce the incidence of disease. In randomized controlled trials (RCTs), the trivalent inactivated vaccine directly reduced the risk of clinical infection by 22% (95% CI: 11–41%) in healthy children [1] and 41% (95% CI: 36–47%) in healthy adults [2]. In households and communities, vaccinating children indirectly reduced the risk of influenza infection in unvaccinated individuals by 5–82% [3,4,5,6]. States is nearly 76.3% in children aged 6–23 months and 43.3% in adults [7], the effective vaccination coverage (after taking efficacy against clinical infections into account) may be approximately 17% for both age groups. If we assume the vaccine is effective against all strains and that protection against clinical infection protects against transmission, current vaccination rates in the United
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
