Individual antibody and T cell responses to vaccination and infection with the 2009 pandemic swine-origin H1N1 influenza virus.

INTRODUCTION

The 2009 swine-origin H1N1 influenza virus (swH1N1) provided an opportunity to study immune responses to a new influenza strain in the context of seasonal influenza vaccination. Our goals were: to assess whether analyzing multiple parameters of immune responsiveness to influenza has an advantage over evaluating hemagglutination inhibition (HAI) titer alone, to determine whether vaccination with the seasonal vaccine induced cross-reactive immunity to swH1N1 in some individuals, and to determine whether the immune response against swH1N1 is higher after infection than vaccination.

METHODS

Antibody and T cell responses were studied in ten subjects who were first immunized with the 2009-2010 seasonal influenza subunit vaccine, then 6 weeks later with the swH1N1 monovalent subunit vaccine. The amount of antibody against native virus glycoproteins, overall avidity of these antibodies, and HAI titer were measured. T cells were evaluated for proliferation and IFNγ secretion in response to the vaccine in vitro. Individuals with influenza-like illness were also evaluated, adding a microplate neuraminidase inhibition (NAI) test.

RESULTS

The immune response to influenza was highly variable and immune parameters did not increase in parallel. The seasonal vaccine induced antibodies recognizing the pandemic virus in 50% of subjects. Antibody affinity and NAI activity to swH1N1 were higher after natural infection than vaccination.

CONCLUSIONS

The evaluation of several immune parameters gives a more complete measure of immune responsiveness to influenza infection or vaccination than the HAI test alone.