Stupid vaccine question

[FloFloFloFloFlo]

The vaccines have a 60-70% efficacy against the delta strain.

So does this mean that if you’re exposed to covid 100 times, the vaccine will stop you getting it 60-70 of those times?

Or does it mean that if 100 people are exposed to covid that 60-70 of them will be protected?

I’m sorry if this is a stupid question!

The vaccine isn’t designed to stop you getting it, it’s designed to stop you getting seriously ill from it if you do get it.

Or does it mean that if 100 people are exposed to covid that 60-70 of them will be protected?

This is how I understand it.
100 fully vaccinated people, of course.

And on average. If you take two random groups of people, you could have 90% protected in one group, and less than 50% in the other. Why? Because it's random. These figures are based on much larger samples of course.

@Randomness12

The vaccine isn’t designed to stop you getting it, it’s designed to stop you getting seriously ill from it if you do get it.

I don't think that was OP's question?

So does this mean that if you’re exposed to covid 100 times, the vaccine will stop you getting it 60-70 of those times?

To expand on why I believe your second statement is correct, it's not about how many time you're exposed to the virus.

Some people (very few) have caught it from a 5 min chat, outdoors, and they might have been vaccinated even.

Others have lived in the same house with positive cases, not even taking any measures, and they never caught the virus, symptomatically or asymptomatically.

It depends on viral load, length of exposure, and one's 'natural immunity' to catching the virus which has been proven as playing a significant part.

Chances are most people have been exposed to this virus, one way or another. But obviously not all of us have caught it.

This explains efficacy quite well:

www.who.int/news-room/feature-stories/detail/vaccine-efficacy-effectiveness-and-protection

Thanks everyone!

This is my understanding…

First, wherever you see an efficacy figure quoted it will be for efficacy at something. Some figures will relate to reduction in hospitalisation and serious illness; others will relate to rates of symptomatic illness.

Then: if you take a number of people who aren’t vaccinated and the same number of people who are, if 100 of the non-vacc group get Covid and 10 are subsequently hospitalised, you would only expect 3-4 to be hospitalised in the vaccinated group* - ie 60-70% fewer if the vaccine were 60-70% effective against hospitalisation. (Or if it referred to efficacy against symptomatic illness then if 100 in the first group got symptomatic illness you’d expect around 30-40 in the vaccinated group)

Hope someone can confirm whether this understanding is correct or not!

Re Delta, my understanding is that estimates can be made based on real world figures but we don’t have clinical trial data as trials were mostly pre-Delta? Which will account for various different figures being flung around.

my question is would that be true only if 100 were shown to have Covid in both groups or would it look at total risk of hospitalisation, not risk of hospitalisation only if* you had developed Covid? Am guessing total risk would make most sense, not risk if you developed it.

It's not a stupid question at all and we don't actually know the answer. It's likely to be a mixture of the two. We know that some people (i.e. immunocompromised) don't get much if any protection from the vaccine, at least for a time. Some lucky few might hit on a particularly neutralising antibody and be 100% immune to current strains. For everyone else it might be a roll of the dice whenever they're exposed.

Gah, poorly edited that! I meant to say "Some lucky few might hit on a particularly neutralising antibody and be 100% immune to current strains, at least for a time"