The Pfizer Vaccine and do people who had COVID already need the vaccine?

[NTorch]

The FDA has a report on the efficacy on the Pfizer vaccine and it is an interesting read.

I don't know why it is dated 12/10, but it can be found here https://www.fda.gov/media/144245/download

There was an interesting piece on p.47 about those who already had it, which basically shows that even in December no one knows much about reinfection:

Effectiveness in individuals previously infected with SARS-CoV-2
The primary endpoint was evaluated in individuals without prior evidence of COVID-19 disease,
and very few cases of confirmed COVID-19 occurred among participants with evidence of
infection prior to vaccination (although more cases occurred in the placebo group compared
with the vaccine group). Therefore, available data are insufficient to make conclusions about
benefit in individuals with prior SARS-CoV-2 infection. However, available data, while limited, do
suggest that previously infected individuals can be at risk of COVID-19 (i.e., reinfection) and
could benefit from vaccination.

[Alexsei]

TL;DR?

Did they directly expose people in the trial to the virus after being vaccinated ?

[Ergel]

TL;DR?

Did they directly expose people in the trial to the virus after being vaccinated ?

No

[NTorch]

From page 27:

Only 3% of participants had evidence of prior infection at study enrollment, and additional
analyses showed that very few COVID-19 cases occurred in these participants over the course
of the entire study (9 in the placebo group and 10 in the BNT162b2 group, only 1 of which
occurred 7 days or more after completion of the vaccination regimen – data not shown). The
placebo group attack rate from enrollment to the November 14, 2020, data cut-off date was
1.3% both for participants without evidence of prior infection at enrollment (259 cases in 19,818
participants) and for participants with evidence of prior infection at enrollment (9 cases in 670
participants). While limited, these data do suggest that previously infected individuals can be at
risk of COVID-19 (i.e., reinfection) and could benefit from vaccination

[Alexsei]

No

So there goes the efficacy

[S209]

So there goes the efficacy

?

[Alexsei]

?

How could you establish the efficacy of the vaccine when you have no control on the exposure of both groups?

[S209]

How could you establish the efficacy of the vaccine when you have no control on the exposure of both groups?

By waiting for a large number of infections to develop, then unblinding the test and seeing how many were in the placebo cohort and how many received the actual vaccine. That’s the procedure used by all major vaccine candidates, and the results have been pretty uniform for Pfizer and Moderna so far.

While your way would have been significantly faster, ethical concerns prevented them from conducting a trial like that.

[PlatinumGuy]

While your way would have been significantly faster, ethical concerns prevented them from conducting a trial like that.

There are claims designing Human Challenge Trials would've actually taken longer than the 2 months it took to reach the efficacy thresholds. Remember, you have to effectively isolate anybody you infect, which would create an enormous logistical burden and severely limit the volunteer pool.

[Alexsei]

By waiting for a large number of infections to develop, then unblinding the test and seeing how many were in the placebo cohort and how many received the actual vaccine. That’s the procedure used by all major vaccine candidates, and the results have been pretty uniform for Pfizer and Moderna so far.

While your way would have been significantly faster, ethical concerns prevented them from conducting a trial like that.

All good, however we know so little about transmission and the data keeps on changing, with these people in the trial likely not eating out in restaurants, wearing masks and practicing social distancing, what does it tell us when one group has 90 infected and the other 11? isn't it scientifically plausible that the results could've been much closer?

If my goal is to establish the efficacy of the vaccine in immunizing the patient against being infected "when exposed" what does the trial tell me? 

[S209]

All good, however we know so little about transmission and the data keeps on changing, with these people in the trial likely not eating out in restaurants, wearing masks and practicing social distancing, what does it tell us when one group has 90 infected and the other 11? isn't it scientifically plausible that the results could've been much closer?

If my goal is to establish the efficacy of the vaccine in immunizing the patient against being infected "when exposed" what does the trial tell me?

I’m not sure you’re understanding the statistical results.

The cohorts were identical in all respects, with the one noted variable being either the vaccine or the placebo having been injected. When one cohort fares significantly better (95% significant) that is sufficient to prove what they are trying to. Obviously the larger the sample size the better but by now we have already seen hundreds of infections across the two studies and the data is holding up.

[S209]

There are claims designing Human Challenge Trials would've actually taken longer than the 2 months it took to reach the efficacy thresholds. Remember, you have to effectively isolate anybody you infect, which would create an enormous logistical burden and severely limit the volunteer pool.

Was the large number of participants necessary for the trials needed to maximize knowledge of safety or efficacy?

[PlatinumGuy]

I’m not sure you’re understanding the statistical results.

The cohorts were identical in all respects, with the one noted variable being either the vaccine or the placebo having been injected. When one cohort fares significantly better (95% significant) that is sufficient to prove what they were trying to. Obviously the larger the sample size the better but we now have seen hundreds of infections across the two studies and the data is holding up.

FWIU, he's claiming the vaccine has only been proven to work against the lower viral loads the trial participants are expected to be exposed to while wearing masks and avoiding most exposure risk. Even if true (there is still full viral load transmission from household members, at the very least), it's a big improvement on zero protection, and the understanding of the mechanism is pretty strong evidence that the vaccine will grant similar immunity from larger viral loads.

Was the large number of participants necessary for the trials needed to maximize knowledge of safety or efficacy?

Both

[Alexsei]

I’m not sure you’re understanding the statistical results.

The cohorts were identical in all respects, with the one noted variable being either the vaccine or the placebo having been injected. When one cohort fares significantly better (95% significant) that is sufficient to prove what they are trying to. Obviously the larger the sample size the better but by now we have already seen hundreds of infections across the two studies and the data is holding up.

We have so many unanswered questions about transmission that, you are correct I do not understand how the statistical results prove the vaccine is 95% effective in immunizing people against the virus.
I'm indeed missing something that's why I posted because I want to be challenged sop that I can understand better

[S209]

We have so many unanswered questions about transmission that, you are correct I do not understand how the statistical results prove the vaccine is 95% effective in immunizing people against the virus.
I'm indeed missing something that's why I posted because I want to be challenged sop that I can understand better

Do you understand what I posted? Can you pinpoint to what exactly you are having difficulty understanding?

FWIU, he's claiming the vaccine has only been proven to work against the lower viral loads the trial participants are expected to be exposed to while wearing masks and avoiding most exposure risk.

I considered that. However from the following I gathered that that was not his question. Please CMIIW- perhaps I misunderstood.

what does it tell us when one group has 90 infected and the other 11? isn't it scientifically plausible that the results could've been much closer?

If my goal is to establish the efficacy of the vaccine in immunizing the patient against being infected "when exposed" what does the trial tell me? 

[aygart]

We have so many unanswered questions about transmission that, you are correct I do not understand how the statistical results prove the vaccine is 95% effective in immunizing people against the virus.
I'm indeed missing something that's why I posted because I want to be challenged sop that I can understand better

That is the purpose of the control group getting the placebo.

[Alexsei]

Do you understand what I posted? Can you pinpoint to what exactly you are having difficulty understanding?I considered that. However from the following I gathered that that was not his question. Please CMIIW- perhaps I misunderstood.

Look at your own circles, have you seen people that weren't infected? can you explain why some people get infected and some don't?

[Alexsei]

That is the purpose of the control group getting the placebo.

How can you ensure both groups have the same exposure? (and have the same susceptibility, which our knowledge is so vague at this point)

[aygart]

How can you ensure both groups have the same exposure? (and have the same susceptibility, which our knowledge is so vague at this point)

You can't ensure so you take large groups and track them out and about to see if there are significant enough differences in results that it would be unlikely to be based on different behaviors.

[Alexsei]

You can't ensure so you take large groups and track them out and about to see if there are significant enough differences in results that it would be unlikely to be based on different behaviors.

So 11/90 in the moderna trial is considered significant?