Interim seasonal influenza vaccine effectiveness estimates as proxy for final estimates: analysis of systematically identified matched pairs of interim/final estimates from test-negative design studies in outpatient settings from 2010/11 to 2018/19

ABSTRACT

Objectives

Limited time for seasonal influenza vaccine development means that the World Health Organization has to consider interim (early) rather than final vaccine effectiveness (VE) estimates in deciding influenza vaccine composition. We assessed agreement between interim and final VE estimates, and factors that may determine a substantial difference (≥10%) between point estimates.

Methods

This was a mixed methods study. We systematically searched, identified, and matched interim/final VE studies of test-negative design (TND) type in outpatient settings after the 2009/10 influenza pandemic. The chi-square statistic (χ2) was used to assess the statistical significance of the difference between paired interim/final VE estimates. We calculated the difference between point estimates and used multivariable logistic regression to assess factors that may determine a substantial difference.

Results

We identified 68 interim/final VE pairs. There was no statistically significant difference between almost all compared pairs. An inconsistent statistical model for interim/final VE estimation and interim VE estimation before the epidemic peak increased the odds of having a substantial difference between estimates.

Conclusion

: Interim influenza VE appears to be sufficient for vaccine composition decision-making. Consistency in interim/final VE estimation, and interim VE estimation during/after epidemic peak may increase agreement between the VE estimates.

KEYWORDS:

• Effectiveness
• seasonal influenza
• systematic review
• test-negative design
• vaccine

Author contributions

Conception/design (G.N.O & S.M.M); Data collection (G.N.O, T.A & F.R); Data analysis/interpretation (G.N.O, C.H.R & S.M.M); Draft manuscript (G.N.O); Manuscript revisions (G.N.O, T.A, F.R, C.H.R & S.M.M); Approval for submission (G.N.O, T.A, F.R, C.H.R & S.M.M).

Supplemental data

Supplemental data for this article can be accessed here.

Acknowledgments

S.M.M has received unrestricted research grants from GlaxoSmithKline, Merck, Sanofi Pasteur, Pfizer and Roche-Assurex for unrelated studies, and fees as an advisory board member for Sanofi Pasteur. The other authors declare that they have no conflicts of interest.

Study funding

No external funding was obtained for this study. S. M. M is supported, in part, by funding from the Canada Research Chairs Program. G. N. O is a recipient of the Manitoba Training Program Fellowship Award, the Centre on Aging Betty Havens Memorial Graduate Fellowship Award, and the Evelyn Shapiro Award, all for health services research.

Declaration of interest

No potential conflict of interest was reported by the authors.