| | | Herd Immunity: The theory that lots of people must catch the bug so lots of people won't catch the bug It's just something that happens — at some point, the R0 number comes down to less than 1. In other words, every infected person will, on average, transmit the disease to less than 1 other person. This will lead to the numbers of infected people coming down - and eventually, the epidemic stops.
It could happen for many reasons - or combinations of them. Pre-existing immunity due to related viruses may make a person less susceptible. Surviving the disease (and acquiring immunity) will do the same. Ditto, the vaccines. When older people stay away from restaurants and crowded places, they also contribute - by denying the virus a chance to infect them.
A curious factoid - it is known that older people often do not mount a strong enough immune response to protect themselves from the flu. Often, however, their response may be strong enough to make the disease milder. Younger people develop stronger immunity - often, enough to protect themselves from the flu. By protecting themselves, they also keep old people safer, via group immunity. |
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