Journal Article

Protective Efficacy of Seasonal Influenza Vaccination against Seasonal and Pandemic Influenza Virus Infection during 2009 in Hong Kong

Benjamin J. Cowling, Sophia Ng, Edward S. K. Ma, Calvin K. Y. Cheng, Winnie Wai, Vicky J. Fang, Kwok-Hung Chan, Dennis K. M. Ip, Susan S. Chiu, J. S. Malik Peiris and Gabriel M. Leung

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 51, issue 12, pages 1370-1379
Published in print December 2010 | ISSN: 1058-4838
Published online December 2010 | e-ISSN: 1537-6591 | DOI: http://dx.doi.org/10.1086/657311
Protective Efficacy of Seasonal Influenza Vaccination against Seasonal and Pandemic Influenza Virus Infection during 2009 in Hong Kong

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Background. The relationship between seasonal influenza vaccine and susceptibility to 2009 pandemic A/H1N1 virus infection is not fully understood.

Methods. One child 6–15 years of age from each of 119 households was randomized to receive 1 dose of inactivated trivalent seasonal influenza vaccine (TIV) or saline placebo in November 2008. Serum samples were collected from study subjects and their household contacts before and 1 month after vaccination (December 2008), after winter (April 2009) and summer influenza (September–October 2009) seasons. Seasonal and pandemic influenza were confirmed by serum hemagglutinination inhibition, viral neutralization titers, and reverse-transcription polymerase chain reaction performed on nasal and throat swab samples collected during illness episodes.

Results. TIV recipients had lower rates of serologically confirmed seasonal A/H1N1 infection (TIV group, 8%; placebo group, 21%; P = .10) and A/H3N2 infection (7% vs 12%; P = .49), but higher rates of pandemic A/H1N1 infection (32% vs 17%; P = .09). In multivariable analysis, those infected with seasonal influenza A during the study had a lower risk of laboratory-confirmed pandemic A/H1N1 infection (adjusted odds ratio [OR], 0.35; 95% confidence interval [CI], 0.14–0.87), and receipt of seasonal TIV was unassociated with risk of pandemic A/H1N1 infection (adjusted OR, 1.11; 95% CI, 0.54–2.26).

Conclusions. TIV protected against strain-matched infection in children. Seasonal influenza infection appeared to confer cross-protection against pandemic influenza. Whether prior seasonal influenza vaccination affects the risk of infection with the pandemic strain requires additional study.

Clinical trials registration. ClinicalTrials.gov number NCT00792051.

Journal Article.  6327 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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