On 03/04/2021 12:12, Dave Plowman (News) wrote:
In article ,
nightjar wrote:
....
Flu mutates at a very high rate, so a vaccine that may have been
effective against one strain one year may not be as effective, if at
all, another year. Unless a vaccine can be demonstrated to be at least
50% effective, it won't be approved.

Don't 'they' guess some time ahead of the flu season and make vaccines
based of that best guess? Which isn't always correct?

The WHO tries to predict which three strains are most likely to be a
threat next season and the manufacturers work to that. As you say, they
don't always get it right, so some years the vaccines provide less
protection than in others.

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Colin Bignell