I'm a vaccine junkie. I love vaccines. I'll take all the vaccines you've got. Watching the needle piercing my flesh...yes, Yes, YES!!!

do you have a history of allergy?
Seem trials were done on subjects who did not have this history .. now they tell us.
Would statisticians call this 'selection bias'?

Do scientists not 'flag implicit assumption'?? 101

What does it even mean? Aren't we supposed to have what's basically an allergic reaction to a vaccine?

Having difficulty interpreting this. Do you mean scientists should become better requirements analysts (ah, the good old days) i.e. less tunnel vision.

“An expert is a person who has made all the mistakes that can be made in a very narrow field.” 

Epidemiology excluded, of course.

With fast evolving viruses you never make the same mistake twice. It will be even hard to tell a success from a failure.

I was wondering what it means to have an allergic reaction to a vaccine. Allergy is a response of the immune system to a factor which isn't threatening. Isn't it basically how vaccines work?

I'm obviously not an expert on that, but trying to reply to katastrofa's point. Imho allergic reaction and immune response are related processes. I believe I read elsewhere that people with allergies often have stronger immune system  

Serious response: try this article

https://www.sciencealert.com/the-oxford ... ific-paper

If the original question was "what is the (math) definition of efficacy?", trackstar's first link illustrates it. Namely, wait for N covid cases in a study of M people. Then N = NV + NP, where NV got the vaccine and NP got the placebo. The study efficacy (and so an estimate of the population efficacy)  is defined as 1 - NV/NP. Of course, separate and related questions are choosing N and M reasonably, and estimating the errors. Easily googleable for the lazy (me), say here

It took 2 days before someone came up with the question 'what is efficacy'?
is it a number?

The efficacy of a vaccine is a percentage reduction in infections in the sample or the population (two different things) upon their vaccination, as above. Definitely a number, a statistical one though.

The efficacy of a vaccine is a percentage reduction in infections in the sample or the population (two different things) upon their vaccination, as above. Definitely a number, a statistical one though.

Nice. 
Have these companies published how they got these numbers?

The 'statistical process' is not rocket  science I guess and you could compare apples with apples. Now it's a drip feed.

The efficacy of a vaccine is a percentage reduction in infections in the sample or the population (two different things) upon their vaccination, as above. Definitely a number, a statistical one though.

Nice. 
Have these companies published how they got these numbers?

The 'statistical process' is not rocket  science I guess and you could compare apples with apples. Now it's a drip feed.

Yes, I believe they used a process commonly referred to as “counting”.

Serious response: try this article

https://www.sciencealert.com/the-oxford ... ific-paper

If the original question was "what is the (math) definition of efficacy?", trackstar's first link illustrates it. Namely, wait for N covid cases in a study of M people. Then N = NV + NP, where NV got the vaccine and NP got the placebo. The study efficacy (and so an estimate of the population efficacy)  is defined as 1 - NV/NP. Of course, separate and related questions are choosing N and M reasonably, and estimating the errors. Easily googleable for the lazy (me), say here

Alan, thank you for sharing a great link! This is the most concise and useful description of the process which I saw so far. 

a good basic book to start reading on basics of vaccines. (I skimmed it in the 90s, possibly better books today )
yes there are good vaccines and bad vaccines. Good vaccines, well compared to what? no action, or ``secret" "herbs"? 

A couple of links to help the research effort here (now that you have a satisfactory definition of efficacy) : )

1) WHO Database of Clinical Trials - International - https://clinicaltrials.gov/ct2/who_table

2) Covid-19 Clinical Research - NIH US - https://www.niaid.nih.gov/diseases-cond ... l-research

3) FDA Guidance for Industry (If you are interested in the policy side) - https://www.fda.gov/media/137926/download

4) Interesting article in Nature - "COVID-19 clinical trials: learning from exceptions in the research chaos" September 22, 2020: https://www.nature.com/articles/s41591-020-1077-z

and finally

5) Analysis of trials - "Analysis of COVID-19 clinical trials: A data-driven, ontology-based, and natural language processing approach" PLOS One September 30 2020 - https://journals.plos.org/plosone/artic ... ne.0239694 

Excerpt from Abstract: "With the novel COVID-19 pandemic disrupting and threatening the lives of millions, researchers and clinicians have been recently conducting clinical trials at an unprecedented rate to learn more about the virus and potential drugs/treatments/vaccines to treat its infection. As a result of the influx of clinical trials, researchers, clinicians, and the lay public, now more than ever, face a significant challenge in keeping up-to-date with the rapid rate of discoveries and advances. To remedy this problem, this research mined the ClinicalTrials.gov corpus to extract COVID-19 related clinical trials, produce unique reports to summarize findings and make the meta-data available via Application Programming Interfaces (APIs)...."

**

So, I had been following the research again for awhile now, but I am taking a vacation from Covid for the weekend!   

Stay safe, wear your masks, no sharing bottles of beer or joints between two or more people.

One bottle, one spleef, one person. Safe enough.

And that's it - good luck!

Added link and corrected a typo.

Спутник V

Спутник V

Let me know when you have digested all of the research finished since say October 2020 and we can talk.  : D

The efficacy of a vaccine is a percentage reduction in infections in the sample or the population (two different things) upon their vaccination, as above. Definitely a number, a statistical one though.

Nice. 
Have these companies published how they got these numbers?

The 'statistical process' is not rocket  science I guess and you could compare apples with apples. Now it's a drip feed.

I'd say it's worse than rocket science. They tested it in a trial in the sample, which often doesn't translate well to the effectiveness in field conditions in the population, where factors like providing reliable freezers need to be included.
Also British apples are different than say Ukrainian apples - they ripen in different conditions, are prone to different plagues... "We have just one world, but we live in different ones".
For the record, I'm not calling against the vaccines in general, and since covid (plus the way it is managed) seems to have a much larger destructive potential than any badly designed vaccine... Of course we can imagine the worst horror scenarios after vaccinations. I imagine that one of scenarios would look like H1N1 epidemics, which simmered down after a year. Then Ford started the - widely considered unnecessary - vaccination program. Just a little snowfall of consciousness...