Is the Pfizer vaccine effective after the first dose?

[odyssey2]

If you look at the cumulative incidence curves available online for both the Pfizer and Moderna vaccines, the curve flattens almost completely 12-14 days after the first dose is given and barely changes at all after the second dose. People are throwing around the “50% immunity” number after the first dose of the Pfizer vaccine, but this seems to come from including the people who got covid within the first two weeks after the first dose, when the vaccine isn’t supposed to be effective at all. Starting at the 12 day mark, the efficacy rate seems to be in the 90-95% range, close to the overall efficacy rate.

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[Lawpy]

The major question is whether vaccines work against covid 19 variants, especially the Variant of Concern

 

[odyssey2]

The major question is whether vaccines work against covid 19 variants, especially the Variant of Concern

Seems likely they would, given that years of mutations would need to accrue to change the spike protein that the vaccine targets.

 

[odyssey2]

Too early to tell. Limited data from the trials estimate 50-80% immunity after 1 dose, but that was not the data they were focused on measuring.

This is what happens when you rush 10+ years of development into 10 months. We simply do not have enough data to know, and it will be another few months of monitoring the vaccine to tell. No scientist would feel comfortable saying the curve is fully flattened after the first dose.

Part of my point was that the “50%” efficacy after first dose being offered is misleading since it’s including people who got sick within the first 1-2 weeks after the first dose. Additionally, Moderna separated out people who only got one dose which had a 92% overall efficacy rate after day 14, and the incidence curves of both Pfizer and Moderna are very similar, flattening out after 10-14 days.
We may not have perfect data but we do have several clinical trials with 40,000 participants each, which so far suggest strong protection after the first dose. Some people seem to think the first dose is only half as effective and I think that’s misleading.
I’m not at all suggesting that people not get the second dose, just that people may be able to breathe a sigh of relief once they get to 2 weeks past the first dose.

 

[DoctwoB]

If you look at the cumulative incidence curves available online for both the Pfizer and Moderna vaccines, the curve flattens almost completely 12-14 days after the first dose is given and barely changes at all after the second dose. People are throwing around the “50% immunity” number after the first dose of the Pfizer vaccine, but this seems to come from including the people who got covid within the first two weeks after the first dose, when the vaccine isn’t supposed to be effective at all. Starting at the 12 day mark, the efficacy rate seems to be in the 90-95% range, close to the overall efficacy rate.

All this is true. The caveat of course is that it was a secondary analysis with limited number of events. Looking specifically at a 1-2 week window with a small N it would be easy for chance to play a big role in the numbers. But the suggestion is that you’re likely protected after 10-14 days.

And remember most of the infections on days 0-10 were likely contracted before or just around the time of vaccination, so you may be protected from “new” exposures started a few days after the vaccine, but that of course is conjecture.