A thread about COVID19 mRNA vaccine second dose timing controversies:

Basically I think it’s honestly a good move to have a flexible (out to 6 week) second dose (and was lobbying for a flexible second dose.)

Rationale:
1) Analysis of trial data of both mRNA vaccines...
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...shows about 93% effectiveness from 2 weeks after the first dose (infections before that could have been incubating before people have had an antibody response)
2) Antibody levels from vaccine are good- they are about 4 fold higher than convalescent levels after infection.
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A bit less strong in elderly potentially though.
3) Some of the trial patients received dose 2 late, as happens, out to 42 days -so there is some data from a longer time period before second dose from Pfizer. Some think out to 3 months is likely fine...
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...but 3 month/longer delays are controversial.
4) Second doses shouldn’t be skipped! Important usually to really lock in a long lasting immune response.
5) The intervals studied in the trials were planned to be short because it’s a pandemic...
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but for some vaccines the second dose at 2 mo is better because of a more mature memory response.
5) Immunologists do not expect antibody to wane within 6 weeks-3 month range anyway as levels are so good (and people are protected from natural infection for longer usually)
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6) Modelling of vaccine supply suggests flexible second dosing can save 25-35% more lives- allows more first doses when there is good supply and if your shipments are delayed you have a bit of wiggle room. I think they’re very good at centralized supply monitoring...
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I think they’ll hold back a variable proportion of supply for dose 2 but not keep 50% in freezer - because it’s protecting people by being in arms not freezers.

And I’m booked for my COVID19 vaccine now. Picked a “dose 2” date in 6 weeks. (Booking site was fine-fixed!)

/fin