On February 17-18, 2011, the World Health Organization convened the 7th meeting on "The Evaluation of Pandemic Influenza Vaccines in Clinical Trials" to review the progress made on pandemic A (H1N1) 2009 vaccines and the evaluation of their effectiveness in the field, especially in children less than 3 years of age and in pregnant women. Other topics to be addressed included a comparison of egg- and cell culture-based influenza vaccines, technical issues related to vaccine strain development and vaccine potency, and the status of development of prototype influenza vaccines using new technologies. Pandemic A (H1N1) vaccines were safe in young children, pregnant women and immunocompromized individuals. Overall effectiveness of inactivated A (H1N1) vaccines for all ages was found to vary between 72% and 100% in different countries and with different vaccine preparations. Effectiveness of pandemic A (H1N1) 2009 live attenuated vaccine was estimated to be approximately 80% in pediatric populations in the USA. A single dose of inactivated vaccine adjuvanted with AS03, MF59 or AF03 induced protective immunity in young children and pregnant women. However, unadjuvanted vaccines as well as low dose adjuvanted vaccines (1.9 μg HA) required two doses to elicit protective antibody levels in these populations. Clinical trials of influenza vaccines developed using new technologies showed they were well tolerated and induced antibody and/or T cell immune responses to viral proteins. Further studies are warranted to validate novel immunological criteria for evaluation and licensing of such new influenza vaccine concepts. On the regulatory side, work should be undertaken to harmonize the results of serological tests used to evaluate the immunogenicity of traditional influenza vaccines.
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