Evaluation of Southern Hemisphere influenza vaccine recommendations

Abstract

In 1999, the World Health Organization switched from annual to semi-annual recommendations for influenza vaccine composition. We compared the antigenic match between recommendations and circulating viruses before and after 1999, in the Northern and Southern Hemispheres. 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 approximately 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.

Figure 1

Percent of isolated and antigenically characterized A/H3N2 influenza viruses that matched the WHO recommended vaccine composition by hemisphere, 1990–2008, based on data described in Table 2. Percent match was calculated by dividing the number of A/H3N2 viruses that matched the vaccine strain (based on the definition of antigenic clusters as in [2, 49]) by the total number of antigenically characterized viruses.

Figure 2

Percent of isolated and antigenically-characterized B influenza viruses that matched the WHO recommended vaccine viruses by hemisphere, 1996–2008, based on data described in Table 2. Percent match was calculated by dividing the number of B viruses that matched the vaccine lineage (influenza B Yamagata or Victoria) by the total number of antigenically characterized viruses.