In 1999, the World Health Organization switched from annual to semiannual recommendations for influenza vaccine composition. We compared the antigenic match between recommendations and circulating viruses before and after 1999. Vaccine match proportion for A/H3N2 viruses increased from 31% to 59% in the Southern hemisphere (P<0.05), and is now comparable to that in the Northern hemisphere. Vaccine match for influenza B decreased from ~100% to 33–54% in both hemispheres (P<0.05), following the unexpected resurgence of influenza B/Victoria in 1997. No estimate was available for influenza A/H1N1. We conclude that semi-annual vaccine recommendations are useful overall and discuss potential ways forward, including a recommendation for the improvement of vaccination policy and influenza surveillance in tropical areas.
【저자키워드】 Influenza, seasonality, Northern hemisphere, southern hemisphere, WHO recommendations, vaccine match, antigenic characteristics,