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Antibody response of healthy children to pandemic A/H1N1/2009 influenza virus

Susanna Esposito1, Cristina Daleno1, Claudia Tagliabue1, Alessia Scala1, Irene Picciolli1, Francesca Taroni1, Carlotta Galeone23, Fausto Baldanti4 and Nicola Principi1*

Author Affiliations

1 Department of Maternal and Pediatric Sciences, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via Commenda 9, 20122 Milan, Italy

2 Department of Epidemiology, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy

3 Department of Occupational Health "Luigi Devoto", University of Milan, Milan, Italy

4 Molecular Virology Unit, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy

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Virology Journal 2011, 8:563  doi:10.1186/1743-422X-8-563

Published: 30 December 2011

Abstract

Background

Little is known about the proportion of pediatric pandemic A/H1N1/2009 influenza cases who showed seroconversion, the magnitude of this seroconversion, or the factors that can affect the antibody level evoked by the pandemic A/H1N1/2009 influenza. Aims of this study were to analyse antibody responses and the factors associated with high antibody titres in a cohort of children with naturally acquired A/H1N1/2009 influenza infection confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR).

Results

Demographic, clinical and virologic data were collected from 69 otherwise healthy children with pandemic A/H1N1/2009 influenza (27 females, mean age ± SD: 5.01 ± 4.55 years). Their antibody levels against pandemic A/H1N1/2009 and seasonal A/H1N1 influenza viruses were evaluated by measuring hemagglutination-inhibiting antibodies using standard assays. Sixty-four patients (92.8%) with pandemic A/H1N1/2009 influenza had A/H1N1/2009 antibody levels of ≥40, whereas only 28/69 (40.6%) were seroprotected against seasonal A/H1N1 influenza virus. Those who were seroprotected against seasonal A/H1N1 virus were significantly older, significantly more often hospitalised, had a diagnosis of pneumonia significantly more frequently, and were significantly more often treated with oseltamivir than those who were not seroprotected (p < 0.05). The children with the most severe disease (assessed on the basis of a need for hospitalisation and a diagnosis of pneumonia) had the highest antibody response against pandemic A/H1N1/2009 influenza virus.

Conclusions

Otherwise healthy children seem to show seroprotective antibody titres after natural infection with pandemic A/H1N1/2009 influenza virus. The strength of the immune response seems to be related to the severity of the disease, but not to previous seasonal A/H1N1 influenza immunity.

Keywords:
Children; Immune response; Influenza; Pandemic A/H1N1/2009 influenza virus; Pediatric infectious diseases