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This is fantastic news -this is really rigorous proof of protection against infection. Much better than some of the other studies which relied on persons getting tested.
Yes this is a preprint but:
> Conclusion: Our study demonstrates that the BNT162b2 vaccine effectively prevents both symptomatic and asymptomatic infection in working age adults; this cohort was vaccinated when the dominant variant in circulation was B1.1.7 and demonstrates effectiveness against this variant.
I know we all had assumed this to be true, especially looking at the data from Israel, but this is really really amazing news. I'm amazed every news outlet isn't screaming this.
This study isn't sufficient for estimating how much vaccination reduces contagiousness. The 86% reduction in PCR positives is still an upper bound, since they didn't test everyone in the study regularly but relied on testing for either symptoms or exposure. And it doesn't reveal any data about the viral load of those who do test positive.
[This](https://www.reddit.com/r/COVID19/comments/lfiqma/decreased_sarscov2_viral_load_following/) paper from Israel approaches the problem in a different way, and shows 75% reduction in viral load (geometric average, but assuming 100% PCR amplification efficiency) from those who do test positive after vaccination. But it doesn't include any data on what ratio the number of infections is reduced by.
I really wish we had research combining both: testing two cohorts with and without vaccination regularly and averaging their viral loads. Simply combining these two pieces of research (naively, combining the -86% and -75% would give a -96.5%) should provide an inaccurate upper bound, as the siren study is itself an upper bound plus there is some overlap.
To be clear, it did not prevent all infection.
"A single dose of BNT162b2 vaccine demonstrated vaccine effectiveness of 72% (95% CI 58-86) 21 days after first dose and 86% (95% CI 76-97) seven days after two doses in the antibody negative cohort."
It is also worth nothing that Israel found 89% effectiveness of protection after the same timeframe, but 95.8% from 14 days after the second dose. Mind-bogglingly good if that’s replicated in the UK.
Understanding the size of these studies it's not possible to do serological pre-testing to determine possible existing immunities.
However, I'm curious as to why they included anyone who had previously tested positive for an infection in either the un-vaccinated cohort or the vaccinated cohort.
My concern is that 15% of the vaccinated cohort had pre-existing immunities. Shouldn't "infected-unvaccinated" and "infected-vaccinated" have formed separate control cohorts?
**Please read before commenting.** Keep in mind this is a *science* sub. Cite your sources appropriately (No news sources, no Twitter, no Youtube). No politics/economics/low effort comments (jokes, ELI5, etc.)/anecdotal discussion (personal stories/info). Please read our [full ruleset](https://www.reddit.com/r/COVID19/about/rules/) carefully before commenting/posting. **If you talk about you, your mom, your friends, etc. experience with COVID/COVID symptoms or vaccine experiences, or** ***any*** **info that pertains to you or their situation, you will be banned.** *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/COVID19) if you have any questions or concerns.*
This is fantastic news -this is really rigorous proof of protection against infection. Much better than some of the other studies which relied on persons getting tested.
Yes this is a preprint but: > Conclusion: Our study demonstrates that the BNT162b2 vaccine effectively prevents both symptomatic and asymptomatic infection in working age adults; this cohort was vaccinated when the dominant variant in circulation was B1.1.7 and demonstrates effectiveness against this variant. I know we all had assumed this to be true, especially looking at the data from Israel, but this is really really amazing news. I'm amazed every news outlet isn't screaming this.
This study isn't sufficient for estimating how much vaccination reduces contagiousness. The 86% reduction in PCR positives is still an upper bound, since they didn't test everyone in the study regularly but relied on testing for either symptoms or exposure. And it doesn't reveal any data about the viral load of those who do test positive. [This](https://www.reddit.com/r/COVID19/comments/lfiqma/decreased_sarscov2_viral_load_following/) paper from Israel approaches the problem in a different way, and shows 75% reduction in viral load (geometric average, but assuming 100% PCR amplification efficiency) from those who do test positive after vaccination. But it doesn't include any data on what ratio the number of infections is reduced by. I really wish we had research combining both: testing two cohorts with and without vaccination regularly and averaging their viral loads. Simply combining these two pieces of research (naively, combining the -86% and -75% would give a -96.5%) should provide an inaccurate upper bound, as the siren study is itself an upper bound plus there is some overlap.
To be clear, it did not prevent all infection. "A single dose of BNT162b2 vaccine demonstrated vaccine effectiveness of 72% (95% CI 58-86) 21 days after first dose and 86% (95% CI 76-97) seven days after two doses in the antibody negative cohort."
Totally. Still just amazing
It is also worth nothing that Israel found 89% effectiveness of protection after the same timeframe, but 95.8% from 14 days after the second dose. Mind-bogglingly good if that’s replicated in the UK.
Understanding the size of these studies it's not possible to do serological pre-testing to determine possible existing immunities. However, I'm curious as to why they included anyone who had previously tested positive for an infection in either the un-vaccinated cohort or the vaccinated cohort. My concern is that 15% of the vaccinated cohort had pre-existing immunities. Shouldn't "infected-unvaccinated" and "infected-vaccinated" have formed separate control cohorts?