Antibody response of healthy children to pandemic A/H1N1/2009 influenza virus.
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.
Department of Maternal and Pediatric Sciences, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via Commenda 9, 20122 Milan, Italy.
Susanna
S
Esposito
Cristina
C
Daleno
Claudia
C
Tagliabue
Alessia
A
Scala
Irene
I
Picciolli
Francesca
F
Taroni
Carlotta
C
Galeone
Fausto
F
Baldanti
Nicola
N
Principi
D000914:Antibodies, Viral / Q000096:biosynthesis / Q000276:immunology*; D000917:Antibody Formation; D000998:Antiviral Agents / Q000008:administration & dosage; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006760:Hospitalization; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007251:Influenza, Human / Q000150:complications / Q000188:drug therapy / Q000453:epidemiology / Q000276:immunology*; D007558:Italy / Q000453:epidemiology; D008297:Male; D053139:Oseltamivir / Q000008:administration & dosage; D058873:Pandemics; D011024:Pneumonia, Viral / Q000188:drug therapy / Q000453:epidemiology / Q000209:etiology / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012720:Severity of Illness Index; D019562:Viral Load
D000914:Antibodies, Viral; D000998:Antiviral Agents; D053139:Oseltamivir