Questa immagine potrebbe avere delle imperfezioni perché è storica o di reportage.
Transmission electron micrograph (TEM) depicted Russian influenza-A H1N1 (A/USSR/90/77 strain) virions, which had been magnified 189, 000x. The 1977-1978 Russian flu epidemic was caused by strain Influenza A/USSR/90/77 (H1N1). It infected mostly children and young adults under 23 because a similar strain was prevalent in 1947-57, causing most adults to have substantial immunity. Because of a striking similarity in the viral RNA of both strains - one which is unlikely to appear in nature due to antigenic drift - it was speculated that the later outbreak was due to a laboratory incident in Russia or Northern China, though this was denied by scientists in those countries. Influenza type A viruses are divided into subtypes based on two proteins on the surface of the virus. These proteins are called hemagglutinin (H) and neuraminidase (N). The current subtypes of influenza A viruses found in people are A(H1N1) and A(H3N2). Influenza B virus is not divided into subtypes. Influenza A (H1N1), A(H3N2), and influenza B strains are included in each year's influenza vaccine. Influenza types A or B viruses cause epidemics of disease almost every winter. In the United States, these winter influenza epidemics can cause illness in 10% to 20% of people and are associated with an average of 36, 000 deaths and 114, 000 hospitalizations per year. Getting a flu shot can prevent illness from types A and B influenza. Influenza type C infections cause a mild respiratory illness and are not thought to cause epidemics. The flu shot does not protect against type C influenza.
