Immunogenicity and Reactogenicity of 1 versus 2 Doses of Trivalent Inactivated Influenza Vaccine in Vaccine-Naive 5-8-Year-Old Children.
Neuzil, Kathleen M. 1,2; Jackson, Lisa A. 4; Nelson, Jennifer 3,4; Klimov, Alexander 6; Cox, Nancy 6; Bridges, Carolyn B. 7; Dunn, John 5; DeStefano, Frank 8; Shay, David 6
[Article] Journal of Infectious Diseases. 194(8):1032-1039, October 15, 2006.

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Background. Two doses of trivalent inactivated influenza vaccine (TIV) are recommended for children <9 years old receiving vaccine for the first time, but compliance is suboptimal. This study assessed the need for a second dose of TIV in this age group.

Methods. In this prospective, open-label study, 232 influenza vaccine-naive 5-8-year-olds enrolled in a health maintenance organization received 2 doses of TIV in fall 2004. Serum for antibody titer measurement was obtained at 3 time points (n=222). Parents completed diaries for 5 days.

Results. Both doses of vaccine were well tolerated. The strongest predictor of a protective antibody response (>=1:40) after 1 dose of TIV was baseline seropositive status. In multivariate analysis adjusting for age, sex, and baseline serostatus, the proportion of children with protective antibody responses was significantly higher after 2 doses than after 1 dose of TIV for each antigen (P<.001, for A/H1N1; P=.01, for A/H3N2; P<.001, for B). Age and sex were not independently predictive of a protective antibody response. Over one-third of children had antibody responses <1:40 for the type B vaccine component, even after 2 doses.

Conclusions. The present study supports the need for 2 doses of TIV in 5-8-year-olds receiving TIV for the first time. Efforts to increase compliance with the 2-dose recommendation are warranted.

(C) Copyright Oxford University Press 2006.