4 ms·

I would assume this is because of how fast flu is evolving and how many strains there are, with different ones predominant in any given year. Covid is (relative

by sershe 6y ago

I would assume this is because of how fast flu is evolving and how many strains there are, with different ones predominant in any given year. Covid is (relatively) stable, so you'd just use the same one.

catalogia 6y ago
If it's stable, wouldn't immunity be stable too? Or is immunity decay a matter of your immune system being unstable, rather than the virus?
- fragmede 6y ago
  In the case of covid, the suspicion is that the former is true. There isn't enough data yet to be able to say one way or the other with any certainty, however.
  - nsnick 6y ago
    The weird thing is the virus has been around for 6 months and no one has caught it twice...