Estimation of the efficacy of live, attenuated influenza vaccine from a two-year, multi-center vaccine trial: implications for influenza epidemic control.
2000 Mar 17
Journal Article
Authors:
Longini, I.M.;
Halloran, M.E.;
Nizam, A.;
Wolff, M.;
Mendelman, P.M.;
Fast, P.E.;
Belshe, R.B.
Secondary:
Vaccine
Volume:
18
Pagination:
1902-9
Issue:
18
PMID:
10699339
DOI:
10.1016/s0264-410x(99)00419-3
Keywords:
Child, Preschool; Double-Blind Method; Humans; Infant; Influenza A Virus; Influenza B virus; Influenza Vaccines; Influenza, Human; Placebo Effect; Treatment Outcome; Vaccines, Attenuated
Abstract:
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.
