How many flu pandemics have there been?
Three worldwide (pandemic) outbreaks of influenza occurred in the 20th century: in 1918, 1957, and 1968. The latter 2 were in the era of modern virology and most thoroughly characterized. All 3 have been informally identified by their presumed sites of origin as Spanish, Asian, and Hong Kong influenza, respectively.
Why do influenza epidemics occur every year?
These viruses spread seasonally each year because of a phenomenon known as antigenic drift: They evolve just enough to evade human immune systems, but not enough to develop into completely new versions of the virus. The H3N2 subtype causes the most disease each year.
Was the common flu ever a pandemic?
The 1918 influenza pandemic was the most severe pandemic in recent history. It was caused by an H1N1 virus with genes of avian origin. Although there is not universal consensus regarding where the virus originated, it spread worldwide during 1918-1919.
Is there a flu pandemic every year?
While flu pandemics are rare, they do occur periodically. There have been four flu pandemics since the beginning of the 20th century, the most severe being the Spanish flu of 1918: 1918 Spanish flu pandemic: Killed approximately 675,000 in the U.S.4 1957 Asian flu pandemic: Caused an estimated 116,000 U.S. deaths5
Why is the flu not considered a pandemic?
An influenza pandemic is a global outbreak of a new influenza A virus. Pandemics happen when new (novel) influenza A viruses emerge which are able to infect people easily and spread from person to person in an efficient and sustained way. The United States is NOT currently experiencing an influenza pandemic.
When is Covid supposed to end?
Estimates of their overall immunity remain low enough that there is still a risk of significant waves of disease. Recent projections suggest that it is likely to take until late 2022 or early 2023 for these countries to achieve high vaccine coverage.