インフルエンザ予防接種は、広まっているウイルスがワクチンとよく一致している場合にもっとも有効である。
インフルエンザウイルスは絶えず変化するため、WHO Global Influenza Surveillance and Response System (GISRS)(世界各地のNational Influenza Centresが連携している)が、ヒトの間で循環しているインフルエンザウイルスを監視している。
WHOは長年、ワクチンの成分についての推奨を半年ごとに更新してきた。
これは、もっとも広まっている3つのウイルスの型(3価/2種類のA型ウイルスと1種類のB型ウイルス)を対象としている。2013-2014の北半球のインフルエンザシーズンの始まりと共に、従来の3価ワクチンに加え、B型ウイルスの第2の型を加えた4価ワクチンの成分についても推奨を開始している。4価のインフルエンザワクチンは、B型インフルエンザウイルスの感染に対して、より幅広い防御効果が期待される。
Prevention
The most effective way to prevent the disease and/or severe outcomes from the illness is vaccination. Safe and effective vaccines are available and have been used for more than 60 years. Among healthy adults, influenza vaccine can provide reasonable protection. However among the elderly, influenza vaccine may be less effective in preventing illness but may reduce severity of disease and incidence of complications and deaths.
Vaccination is especially important for people at higher risk of serious influenza complications, and for people who live with or care for high risk individuals.
WHO recommends annual vaccination for:
pregnant women at any stage of pregnancy
children aged 6 months to 5 years
elderly individuals (≥65 years of age)
individuals with chronic medical conditions
health-care workers.
Influenza vaccination is most effective when circulating viruses are well-matched with vaccine viruses. Influenza viruses are constantly changing, and the WHO Global Influenza Surveillance and Response System (GISRS) – a partnership of National Influenza Centres around the world –monitors the influenza viruses circulating in humans.
For many years WHO has updated its recommendation on vaccine composition biannually that targets the 3 (trivalent) most representative virus types in circulation (two subtypes of influenza A viruses and one B virus). Starting with the 2013-2014 northern hemisphere influenza season, quadrivalent vaccine composition has been recommended with a second influenza B virus in addition to the viruses in the conventional trivalent vaccines. Quadrivalent influenza vaccines are expected to provide wider protection against influenza B virus infections.