The best case with mass immunity is that R drops below 0 and the virus burns itself out.
The worst case is that immunity primes the body for a massive and lethal immune system overreaction if the virus returns and/or mutates. This seems to have happened in 1918, which is why the second wave was more deadly.
Generally viruses seem to become less lethal over time, so this is rare and unlikely - and we'd be very unlucky indeed if it happened now.
But it isn't entirely impossible. The smart thing to do would be to have some high-quality monitoring in place to catch it if it starts happening, with high quality contingency planning for an international response.
The worst case is that immunity primes the body for a massive and lethal immune system overreaction if the virus returns and/or mutates. This seems to have happened in 1918, which is why the second wave was more deadly.
Generally viruses seem to become less lethal over time, so this is rare and unlikely - and we'd be very unlucky indeed if it happened now.
But it isn't entirely impossible. The smart thing to do would be to have some high-quality monitoring in place to catch it if it starts happening, with high quality contingency planning for an international response.
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