Immunogenicity and reactogenicity of 1 versus 2 doses of trivalent inactivated influenza vaccine in vaccine-naive 5-8-year-old children.
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 (> or =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.
Neuzil
Kathleen M
KM
Program for Appropriate Technology in Health, School of Medicine, University of Washington, Seattle, Seattle, WA 98107, USA. kneuzil@path.org
Jackson
Lisa A
LA
Nelson
Jennifer
J
Klimov
Alexander
A
Cox
Nancy
N
Bridges
Carolyn B
CB
Dunn
John
J
DeStefano
Frank
F
Shay
David
D
D000914:Antibodies, Viral / Q000097:blood; D002648:Child; D004334:Drug Administration Schedule; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007115:Immunization Schedule; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology; D009980:Influenza A virus / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000009:adverse effects; D007251:Influenza, Human / Q000097:blood / Q000517:prevention & control*; D007273:Injections, Intramuscular; D008297:Male; D010349:Patient Compliance; D011446:Prospective Studies; D014611:Vaccination / Q000379:methods*; D015164:Vaccines, Inactivated / Q000008:administration & dosage / Q000009:adverse effects; D014861:Washington
D000914:Antibodies, Viral; D007252:Influenza Vaccines; D015164:Vaccines, Inactivated