Immunogenicity and safety of pandemic influenza A (H1N1) 2009 vaccine: systematic review and meta-analysis.

The emergence of the 2009 H1N1 pandemic has highlighted the need to have immunogenicity and safety data on the new pandemic vaccines. There is already considerable heterogeneity in the types of vaccine available and of study performed around the world. A systematic review and meta-analysis is needed to assess the immunogenicity and safety of pandemic influenza A (H1N1) 2009 vaccines. We searched Medline, EMBASE, the Cochrane Library and other online databases up to 1st October 2010 for studies in any language comparing different pandemic H1N1 vaccines, with or without placebo, in healthy populations aged at least 6 months. The primary outcome was seroprotection according to haemagglutination inhibition (HI). Safety outcomes were adverse events. Meta-analysis was performed for the primary outcome. We identified 18 articles, 1 only on safety and 17 on immunogenicity, although 1 was a duplicate. We included 16 articles in the meta-analysis, covering 17,921 subjects. Adequate seroprotection (≥70%) was almost invariably achieved in all age groups, and even after one dose and at low antigen content (except in children under 3 years receiving one dose of non-adjuvanted vaccine). Non-adjuvanted vaccine from international companies and adjuvanted vaccines containing oil in water emulsion (e.g. AS03, MF59), rather than aluminium, performed better. Two serious vaccination-associated adverse events were reported, both of which resolved fully. No death or case of Guillain-Barré syndrome was reported. The pandemic influenza (H1N1) 2009 vaccine, with or without adjuvant, appears generally to be seroprotective after just one dose and safe among healthy populations aged ≥36 months; very young children (6-35 months) may need to receive two doses of non-adjuvanted vaccine or one dose of AS03(A/B)-adjuvanted product to achieve seroprotection.