Some info on vaccine efficacy. We tend to make the mistake of 95% efficacy (Pfizer) being 95 out of 100 is protected from the disease while 5 out of 100 will get infected/succumb to disease.
But that’s not how vaccine efficacy works. So how did we get that 95%?
Consider these numbers. The Pfizer P3 trial had 43,661 participants.
Total was split into half, each group received the placebo or the vaccine. The placebo group had 162 symptomatic infection & the vaccine group had 8.
We then can calculate the infection risk. 0.74% vs 0.04%.
To get vaccine efficacy, first we get the risk difference between the two groups.
This means the vaccine reduces infection risk by 0.7 percentage point. But this is not efficacy.
Efficacy is dividing by original infection risk x 100%. Now u get the 95%.
Another way to calculate v.efficacy is to use risk ratio. Basically just take the number of infected in both groups, get the ratio and make it into a %.
So what does 95% means? It means the vaccine reduces the risk of getting the disease by 95%. That’s an incredible number.
Typo : 43,660 total participants. Lol. That is why I need a calculator.
And I must stress again, vaccine efficacy is a lab result in a controlled environment. What we want to look at eventually is vaccine effectiveness. Low efficacy doesnt automatically mean low effectiveness.
If we vaccinate enough, low efficacy vaccines will have high impact.
Linking my posts on vaccine efficacy vs effectiveness here.
We shouldn’t be too fixated on vaccine efficacy. What ultimately is important (& I suspect most of us are talking about) is vaccine effectiveness (VE).
Vaccine efficacy is % of reduction of disease in a vaccinated vs unvaccinated group in a trial.
VE is the real world impact.
V.efficacy measures individual protection in a controlled environment while VE looks at how protected is a population after vaccination. There is a whole host of factors influencing it.
And not necessarily v.efficacy is directly proportional to VE.
Focusing on only efficacy will distract us from implementing a good vaccination plan to maximise effectiveness.
Factors like administration, cold chain, coverage (which impacts herd immunity) all can greatly increase effectiveness, which is what we want.
Always amusing to see men (or rather boys) trying to use declining fertility of women by showing fertility rates to justify that women should marry young.
Firstly, reproduction is not the only purpose in life or partnerships/marriage.
Secondly, they are reading the data wrong.
Fertility rates (broadly) is defined as avg number of children born by a woman in her reproductive years over her lifetime. It measure a period, not the cohort’s metric.
And number of children born means u need the man as well, so the equal & opposite cohort to see is the men.
Blaming women biology for low fertility rates or high risk pregnancies in older women is lazy & ignorant.
Fertility rates drop in older women because their male partners are older too, therefore time to conception is later.