Evaluations for in vitro correlates of immunogenicity of inactivated influenza a H5, H7 and H9 vaccines in humans

PLoS One. 2012;7(12):e50830. doi: 10.1371/journal.pone.0050830. Epub 2012 Dec 11.


Background: Serum antibody responses in humans to inactivated influenza A (H5N1), (H9N2) and A (H7) vaccines have been varied but frequently low, particularly for subunit vaccines without adjuvant despite hemagglutinin (HA) concentrations expected to induce good responses.

Design: To help understand the low responses to subunit vaccines, we evaluated influenza A (H5N1), (H9N2), (H7N7) vaccines and 2009 pandemic (H1N1) vaccines for antigen uptake, processing and presentation by dendritic cells to T cells, conformation of vaccine HA in antibody binding assays and gel analyses, HA titers with different red blood cells, and vaccine morphology in electron micrographs (EM).

Results: Antigen uptake, processing and presentation of H5, H7, H9 and H1 vaccine preparations evaluated in humans appeared normal. No differences were detected in antibody interactions with vaccine and matched virus; although H7 trimer was not detected in western blots, no abnormalities in the conformation of the HA antigens were identified. The lowest HA titers for the vaccines were <1:4 for the H7 vaccine and 1:661 for an H9 vaccine; these vaccines induced the fewest antibody responses. A (H1N1) vaccines were the most immunogenic in humans; intact virus and virus pieces were prominent in EM. A good immunogenic A (H9N2) vaccine contained primarily particles of viral membrane with external HA and NA. A (H5N1) vaccines intermediate in immunogenicity were mostly indistinct structural units with stellates; the least immunogenic A (H7N7) vaccine contained mostly small 5 to 20 nm structures.

Summary: Antigen uptake, processing and presentation to human T cells and conformation of the HA appeared normal for each inactivated influenza A vaccine. Low HA titer was associated with low immunogenicity and presence of particles or split virus pieces was associated with higher immunogenicity.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Antibodies, Viral / blood
  • Antibodies, Viral / immunology
  • Antigen Presentation / immunology
  • Birds / immunology
  • Birds / virology
  • Hemagglutination Inhibition Tests
  • Humans
  • Influenza A Virus, H5N1 Subtype / immunology
  • Influenza A Virus, H7N7 Subtype / immunology
  • Influenza A Virus, H9N2 Subtype / immunology
  • Influenza Vaccines* / administration & dosage
  • Influenza Vaccines* / immunology
  • Influenza in Birds* / immunology
  • Influenza in Birds* / prevention & control
  • Influenza, Human* / immunology
  • Influenza, Human* / prevention & control
  • Vaccines, Inactivated* / administration & dosage
  • Vaccines, Inactivated* / immunology


  • Antibodies, Viral
  • Influenza Vaccines
  • Vaccines, Inactivated