American Journal of Epidemiology Advance Access originally published online on October 29, 2008
American Journal of Epidemiology 2008 168(12):1343-1352; doi:10.1093/aje/kwn259
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Estimating Influenza Vaccine Efficacy From Challenge and Community-based Study Data
Correspondence to Dr. Ira M. Longini, Jr., Program in Biostatistics and Biomathematics, Vaccine and Infectious Disease Institute, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N, Seattle, WA 98109 (e-mail: longini{at}scharp.org).
Received for publication April 24, 2008. Accepted for publication July 28, 2008.
In this paper, the authors provide estimates of 4 measures of vaccine efficacy for live, attenuated and inactivated influenza vaccine based on secondary analysis of 5 experimental influenza challenge studies in seronegative adults and community-based vaccine trials. The 4 vaccine efficacy measures are for susceptibility (VES), symptomatic illness given infection (VEP), infection and illness (VESP), and infectiousness (VEI). The authors also propose a combined (VEC) measure of the reduction in transmission in the entire population based on all of the above efficacy measures. Live influenza vaccine and inactivated vaccine provided similar protection against laboratory-confirmed infection (for live vaccine: VES = 41%, 95% confidence interval (CI): 15, 66; for inactivated vaccine: VES = 43%, 95% CI: 8, 79). Live vaccine had a higher efficacy for illness given infection (VEP = 67%, 95% CI: 24, 100) than inactivated vaccine (VEP = 29%, 95% CI: –19, 76), although the difference was not statistically significant. VESP for the live vaccine was higher than for the inactivated vaccine. VEI estimates were particularly low for these influenza vaccines. VESP and VEC can remain high for both vaccines, even when VEI is relatively low, as long as the other 2 measures of vaccine efficacy are relatively high.
communicable disease control; immunization; influenza, human; influenza vaccines; models, theoretical; research design
Abbreviations: AR, attack rate; CI, confidence interval; RR, relative risk; VE, vaccine efficacy; VEC, combined vaccine efficacy; VEI, vaccine efficacy for infectiousness; VEP, vaccine efficacy for illness given infection; VES, vaccine efficacy for susceptibility; VESP, vaccine efficacy for infection-confirmed influenza illness