Estimation of the efficacy of live, attenuated influenza vaccine from a two-year, multi-center vaccine trial: implications for influenza epidemic control.
The authors provide an analysis of data from a two-year (1996-1998), multicenter (ten US cities), double-blinded, placebo-controlled influenza vaccine trial in children. The vaccine was the trivalent cold-adapted influenza vaccine. Estimates are made of the vaccine efficacy for susceptibility to culture-confirmed influenza (VE(S)) while taking inter-center variability in the risk of infection into account. Our overall estimate of VE(S) against influenza is 0.92 (95% confidence interval (CI) 0.89-0.94). In addition, for the second year, although the vaccine contained antigen for A/Wuhan-like (H3N2), the estimated VE(S) for epidemic variant A/Sydney-like (H3N2) was 0.89 (95% CI 0.81-0.94). Thus, the vaccine showed a high degree of protection against a variant not closely matched to the vaccine antigen. With regard to natural immunity, an influenza A infection in the first year reduces the estimated risk of an influenza A infection in the second year by a factor of 0.88 (95% CI 0.21-0.98). When comparing year 1 to year 2, there is a negative correlation of -0.50 in the center-specific attack rates in the placebo groups. This is consistent with the theory that natural immunity provides overall community protection to children. The authors argue that mass vaccination of 70% of the children with the cold-adapted influenza vaccine could provide substantial protection to the community at large.
Longini
I M
IM
Department of Biostatistics, The Rollins School of Public Health, Emory University, Atlanta, GA, USA. longini@sph.emory.edu
Halloran
M E
ME
Nizam
A
A
Wolff
M
M
Mendelman
P M
PM
Fast
P E
PE
Belshe
R B
RB
D002675:Child, Preschool; D004311:Double-Blind Method; D006801:Humans; D007223:Infant; D009980:Influenza A virus / Q000276:immunology; D009981:Influenza B virus / Q000276:immunology; D007252:Influenza Vaccines / Q000276:immunology / Q000627:therapeutic use*; D007251:Influenza, Human / Q000276:immunology / Q000517:prevention & control*; D015990:Placebo Effect; D016896:Treatment Outcome; D014613:Vaccines, Attenuated / Q000276:immunology / Q000627:therapeutic use
D007252:Influenza Vaccines; D014613:Vaccines, Attenuated