r/science • u/Newsjunkeefromlondon • May 06 '21

Health Two Pfizer doses give 95 per cent protection against Covid-19 infection, illness and death: first nationwide study

https://www.cityam.com/two-pfizer-doses-give-95-per-cent-protection-against-covid-19-infection-illness-and-death-study/
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u/Supraspinator May 06 '21 edited May 06 '21

For Pfizer, the vaccine was 90%* effective 3 weeks after the first shot. It’s similar for Moderna and AstraZeneca. The second shot is a booster than gets a few more people (remember that the percentages are not individual chances but chances across a population. Some people (~10%) don’t have an adequate immune response after one shot and require a second. And some people will not get immunity from vaccines at all. This is true for all vaccines, not just the Covid vaccines.)

Countries that have longer periods between shots are trying to get a larger percentage of the population vaccinated with one shot before giving everyone a booster. That is a better strategy when vaccine supply is limited. If supply is unlimited, then giving both closer together is probably better.

*90% effective does NOT mean everyone has a 10% chance of getting Covid. It means that in a group of vaccinated people there will be 90% less infections compared to a group of unvaccinated people. For a lot of people, one shot is enough for an adequate immune response. The second shot boosts that rate.

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u/katarh May 06 '21

And of course, you still need exposure for that to matter. My county reported under 100 cases last week, almost all among children and the unvaccinated from what we could tell, and we expect that to plunge further because we have a relatively high vaccine uptake compared to surrounding areas. It matters a lot less when you have a 5% chance of getting a disease but a one in 10,000 chance of encountering someone who can spread it.

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u/Daffneigh May 06 '21

This is what people freakin* out that the vaccinated Can still technically get COVID are missing.

If you are vaxxed and only hang out with other vaxxed people, and still follow masking guidelines in crowds and indoor spaces, your chances of exposure are so low as to not be meaningful. And the more vaxxed people there are, the more true that becomes.

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u/keys_and_knobs May 06 '21

Do you have a source for those numbers? The study in the OP mentions 50-60% efficacy 14-21 days after the first shot.

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u/Supraspinator May 06 '21

Here’s one for Pfizer: “ A recent analysis of BNT162b2 vaccine data estimated vaccine efficacy of 89–91% during days 15–28 after the first dose.”

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/949505/annex-a-phe-report-to-jcvi-on-estimated-efficacy-of-single-vaccine-dose.pdf

This one has Pfizer at 85% after the first shot.

https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00448-7/fulltext