The History of Measles and Vaccine Development.

Measles is one of the oldest human diseases, but the fact that it was separate from smallpox, scarlatina and rubella was only disclosed a century ago. It is extremely contagious, as the infection may spread for up to 4 days before the first symptoms appear. One patient may infect 12-18 secondary cases, who then spread the infection further. Before the vaccine era, measles caused 2-3 million deaths a year, with remote populations facing chaotic consequences from epidemics. Safe and inexpensive live-virus vaccines, often combined with mumps and rubella components, have been available for 50 years. The global death toll first dropped below 100 000 per year in 2021, but setbacks have been seen in many countries, including Europe. High mortality is mainly due to immune amnesia, as previously acquired memory is partly disturbed because of the elimination of T and B cells. Impaired protection from pathogens other than measles recovers slowly in subsequent years. Measles is almost exclusively a human infection, which is potentially eradicable with vaccinations. It warrants two doses, especially when contacts with natural measles are minimal or lacking. The World Health Organization is running a measles and rubella elimination program, but current vaccination levels will make that difficult.