The global circulation of seasonal influenza A (H3N2) viruses.

Antigenic and genetic analysis of the hemagglutinin of approximately 13,000 human influenza A (H3N2) viruses from six continents during 2002-2007 revealed that there was continuous circulation in east and Southeast Asia (E-SE Asia) via a region-wide network of temporally overlapping epidemics and that epidemics in the temperate regions were seeded from this network each year. Seed strains generally first reached Oceania, North America, and Europe, and later South America. This evidence suggests that once A (H3N2) viruses leave E-SE Asia, they are unlikely to contribute to long-term viral evolution. If the trends observed during this period are an accurate representation of overall patterns of spread, then the antigenic characteristics of A (H3N2) viruses outside E-SE Asia may be forecast each year based on surveillance within E-SE Asia, with consequent improvements to vaccine strain selection.

Influenza vaccine strain selection and recent studies on the global migration of seasonal influenza viruses.

Annual influenza epidemics in humans affect 5-15% of the population, causing an estimated half million deaths worldwide per year [Stohr K. Influenza-WHO cares. Lancet Infectious Diseases 2002;2(9):517]. The virus can infect this proportion of people year after year because the virus has an extensive capacity to evolve and thus evade the immune response. For example, since the influenza A(H3N2) subtype entered the human population in 1968 the A(H3N2) component of the influenza vaccine has had to be updated almost 30 times to track the evolution of the viruses and remain effective. The World Health Organization Global Influenza Surveillance Network (WHO GISN) tracks and analyzes the evolution and epidemiology of influenza viruses for the primary purpose of vaccine strain selection and to improve the strain selection process through studies aimed at better understanding virus evolution and epidemiology. Here we give an overview of the strain selection process and outline recent investigations into the global migration of seasonal influenza viruses.

Antigenic and genomic relation between human influenza A (h3N2)viruses circulating in Argentina during 1998 and the H3N2 vaccine component

Objective. Due to the lack of correlation from 1994 to 1997 between the A H3N2 componet of the influenza vaccine recomended for this period and the circulating viruses in Argentina, we decided to study the antigenic and genomic relationships of the 1998 A H3N2 Argentine circulating strains with the corresponding vaccine component for that year as recomemded by the World Health Organization (WHO). Methods. We selected 18 influenza A H3N2 strains isolated in Argentina during 1998 to carry out an antigenic and genomic study of their hemagglutinin (HA)AND NEURAMINIDASE (NA)protein. For the genomic study we added 3 isolates froms Uruguay. We compared the Argentine and and Uruguayan strains with available reference strains. Results. We found that all18 strins from Argentina were similar to the A/Sydney/597 (H3N2)strain, as opposed to thr A/wUHAM/395/95 (H3N2) strain, which was the vaccine componet. This result was confirmed by the genomic study. Conclusions. The approach that we applied in Argentina has impoved the quality and quantity of information about influenza in the most appropriate vaccine components each year and provide individuals with the best possible protection against influenza