Friday, July 10, 2020
"Herd immunity" can happen once a large part of a population"say 70-90%"develops immunity to a disease. This generally happens by infection (conferring natural immunity) or vaccination. Herd immunity can help slow or stop a disease's spread, but many people may die before it happens.
It is currently unclear how herd immunity could happen for COVID-19. For example, the data are insufficient to show how much immunity infection confers, or whether it's enough to prevent re-infection. How long any immunity will last is also unknown. Related viruses confer some immunity after infection, but that immunity doesn't seem to last longer than a year.
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