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J Infect Dis. (2014) doi: 10.1093/infdis/jiu186 First published online: March 26, 2014
Association between antibody titers and protection against influenza virus infection within households
Tim K. Tsang1,
Simon Cauchemez2,
R. A. P. Mahen Perera3,4,
Guy Freeman1,
Vicky J. Fang1,
Dennis K. M. Ip5,
Gabriel M. Leung5,
J. S. Malik Peiris3,4 and
Benjamin J. Cowling1
+ Author Affiliations
1Division of Epidemiology and Biostatistics, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China
2Mathematical Modelling of Infectious Diseases Unit, Institut Pasteur, Paris
3Division of Public Health Laboratory Sciences, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
4Centre for Influenza Research, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
5Division of Community Medicine and Public Health Practice, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
Corresponding author: Dr Benjamin J Cowling, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong. Tel: +852 3906 2011; Fax: +852 3520 1945; email: bcowling@hku.hk
Contact information for an alternate corresponding author: Dennis K. M. Ip, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong. Tel: +852 3906 2012; Fax: +852 3520 1945; email: dkmip@hku.hk
Abstract
Background. Previous studies have established that antibody titer measured by the hemagglutination-inhibiting (HAI) assay is correlated with protection against influenza virus infection, with an HAI titer of 1:40 generally associated with 50% protection.
Methods. We recruited index cases with confirmed influenza virus infection from outpatient clinics, and followed up their household contacts for 7-10 days to identify secondary infections. Sera collected from a subset of household contacts were tested by HAI and microneutralization (MN) assays against prevalent influenza viruses. We analysed the data using an individual hazard-based transmission model that adjusted for age and vaccination history.
Results. Compared to a reference group with antibody titers <1:10, we found that HAI titers of 1:40 against influenza A(H1N1) and A(H3N2) were associated with 31% (95% CI: 13% to 46%) and 31% (CI: 1% to 53%) protection against PCR-confirmed A(H1N1) and A(H3N2) virus infection, respectively, while a MN titer of 1:40 against A(H3N2) was associated with 49% (95% CI: 7% to 81%) protection against PCR-confirmed A(H3N2) virus infection.
Conclusions. An HAI titer of 1:40 was associated with substantially less than 50% protection against PCR-confirmed influenza virus infection within households, perhaps because of exposures of greater duration or intensity in that confined setting.
Association between antibody titers and protection against influenza virus infection within households
Tim K. Tsang1,
Simon Cauchemez2,
R. A. P. Mahen Perera3,4,
Guy Freeman1,
Vicky J. Fang1,
Dennis K. M. Ip5,
Gabriel M. Leung5,
J. S. Malik Peiris3,4 and
Benjamin J. Cowling1
+ Author Affiliations
1Division of Epidemiology and Biostatistics, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China
2Mathematical Modelling of Infectious Diseases Unit, Institut Pasteur, Paris
3Division of Public Health Laboratory Sciences, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
4Centre for Influenza Research, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
5Division of Community Medicine and Public Health Practice, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
Corresponding author: Dr Benjamin J Cowling, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong. Tel: +852 3906 2011; Fax: +852 3520 1945; email: bcowling@hku.hk
Contact information for an alternate corresponding author: Dennis K. M. Ip, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong. Tel: +852 3906 2012; Fax: +852 3520 1945; email: dkmip@hku.hk
Abstract
Background. Previous studies have established that antibody titer measured by the hemagglutination-inhibiting (HAI) assay is correlated with protection against influenza virus infection, with an HAI titer of 1:40 generally associated with 50% protection.
Methods. We recruited index cases with confirmed influenza virus infection from outpatient clinics, and followed up their household contacts for 7-10 days to identify secondary infections. Sera collected from a subset of household contacts were tested by HAI and microneutralization (MN) assays against prevalent influenza viruses. We analysed the data using an individual hazard-based transmission model that adjusted for age and vaccination history.
Results. Compared to a reference group with antibody titers <1:10, we found that HAI titers of 1:40 against influenza A(H1N1) and A(H3N2) were associated with 31% (95% CI: 13% to 46%) and 31% (CI: 1% to 53%) protection against PCR-confirmed A(H1N1) and A(H3N2) virus infection, respectively, while a MN titer of 1:40 against A(H3N2) was associated with 49% (95% CI: 7% to 81%) protection against PCR-confirmed A(H3N2) virus infection.
Conclusions. An HAI titer of 1:40 was associated with substantially less than 50% protection against PCR-confirmed influenza virus infection within households, perhaps because of exposures of greater duration or intensity in that confined setting.
