ABSTRACT
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.
Subject(s)
Disease Outbreaks , Hemagglutinin Glycoproteins, Influenza Virus/immunology , Influenza A Virus, H3N2 Subtype , Influenza, Human/epidemiology , Antigenic Variation , Asia/epidemiology , Asia, Southeastern/epidemiology , Europe/epidemiology , Evolution, Molecular , Forecasting , Hemagglutinin Glycoproteins, Influenza Virus/genetics , Humans , Influenza A Virus, H3N2 Subtype/classification , Influenza A Virus, H3N2 Subtype/genetics , Influenza A Virus, H3N2 Subtype/immunology , Influenza A Virus, H3N2 Subtype/isolation & purification , Influenza Vaccines , Influenza, Human/virology , North America/epidemiology , Oceania , Phylogeny , Population Surveillance , Seasons , South America/epidemiologyABSTRACT
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.
Subject(s)
Influenza A Virus, H3N2 Subtype/immunology , Influenza Vaccines/immunology , Influenza, Human/epidemiology , Influenza, Human/prevention & control , HumansABSTRACT
Like other medicine, all vaccines have some side effects or complications; in general the incidence and severity of complications is lower than for pharmaceuticals. When considered on a population basis, the incidence of serious complications of vaccination is minute, when compared with the outcome of natural infection. Enlightened governments, which promote immunisation as a means of minimising the impact of infectious diseases in their communities, also accept the responsibility for any adverse events which can be demonstrated to be vaccine related, and provide compensation and care for people who are affected.
