Estimation of reduction in influenza vaccine effectiveness due to egg-adaptation changes—systematic literature review and expert consensus

Raul Ortiz de Lejarazu-Leonardo, Emanuele Montomoli, Radek Wojcik*, Solomon Christopher, Anne Mosnier, Elena Pariani, Antoni Trilla Garcia, Helmut Fickenscher, Barbara C. Gärtner, Ravi Jandhyala, Maria Zambon, Catherine Moore

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

4 Citations (Scopus)


Background: Influenza vaccines are the main tool to prevent morbidity and mortality of the disease; however, egg adaptations associated with the choice of the manufacturing process may reduce their effectiveness. This study aimed to estimate the impact of egg adaptations and antigenic drift on the effectiveness of trivalent (TIV) and quadrivalent (QIV) influenza vaccines. Methods: Nine experts in influenza virology were recruited into a Delphi-style exercise. In the first round, the experts were asked to answer questions on the impact of antigenic drift and egg adaptations on vaccine match (VM) and influenza vaccine effectiveness (IVE). In the second round, the experts were presented with the data from a systematic literature review on the same subject and aggregated experts’ responses to round one questions. The experts were asked to review and confirm or amend their responses before the final summary statistics were calculated. Results: The experts estimated that, across Europe, the egg adaptations reduce, on average, VM to circulating viruses by 7–21% and reduce IVE by 4–16%. According to the experts, antigenic drift results in a similar impact on VM (8–24%) and IVE (5–20%). The highest reduction in IVE was estimated for the influenza virus A(H3N2) subtype for the under 65 age group. When asked about the frequency of the phenomena, the experts indicated that, on average, between the 2014 and 19 seasons, egg adaptation and antigenic drift were significant enough to impact IVE that occurred in two and three out of five seasons, respectively. They also agreed that this pattern is likely to reoccur in future seasons. Conclusions: Expert estimates suggest there is a potential for 9% on average (weighted average of “All strains” over three age groups adjusted by population size) and up to a 16% increase in IVE (against A(H3N2), the <65 age group) if egg adaptations that arise when employing the traditional egg-based manufacturing process are avoided.

Original languageEnglish
Article number1255
Number of pages14
Issue number11
Publication statusPublished - Nov 2021

Bibliographical note

Publisher Copyright:
© 2021 by the authorsLicensee MDPI, Basel, Switzerland.


  • Antigenic
  • Drift
  • Effectiveness
  • Egg adaptations
  • Influenza
  • Vaccination


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