• The pH1N1 vaccines provide unexpectedly good immune responses.
• Oil-in-water emulsion adjuvants, such as AS03 and MF59, significantly increase immunogenicity of the inactivated split pH1N1 vaccine, allowing a reduction in the dose of hemagglutinin (HA) antigen needed to provide protection.
• Aluminum adjuvant-based pH1N1 vaccines had limited effects on immune response.
• Results from a limited number of published and unpublished studies suggest impressive estimates of pH1N1 vaccine effectiveness (VE).
• The overall safety of the pH1N1 vaccine has been confirmed.
• These findings support the use of either two doses of unadjuvanted pH1N1 vaccine containing 7.5 µg HA administered 21 days apart or one dose of AS03-adjuvanted pH1N1 vaccine containing 1.9 µg of HA to provide adequate protection in children less than 9 years of age.
• The inherent trade-off between community-level risk versus individual-level risk warrants recognition.