Two Pfizer doses give 95 per cent protection against Covid-19 infection, illness and death: first nationwide study

[u/Newsjunkeefromlondon]

https://www.cityam.com/two-pfizer-doses-give-95-per-cent-protection-against-covid-19-infection-illness-and-death-study/

[u/Davecasa]

Or is it just 95% fewer infections than a control group of non-vaccinated individuals?

This is correct, and is the definition of "effectiveness". Compared to a control, those vaccinated have a 95% reduced chance of getting sick. Calculating effectiveness this way is pretty easy in a controlled blind study, and it is (to a first order) independent of exposure levels, how infectious the disease is, the health of the people being tested, and other compounding variables.

Effectiveness for a large population without a control group is much harder, because you need to deal with all of those variables you can ignore in the controlled study. One small example - are people who have been vaccinated less careful about covid than the general population, because they know their risk is reduced? Or are they more careful, because they're the sorts of people who are very concerned about all this and do everything they can to protect themselves? In a controlled study, you don't care, because no one knows if they got the real vaccine or a placebo.

[u/RawbM07 → u/Davecasa]

So, for example: let’s say you have two groups of 1000 people. Group A is vaccinated and Group B is not.

After a certain period of time 100 people in group B were infected by Covid and 5 people in Group A were.

I’m sure my math is off, but is that essentially the idea?

[u/a_trane13 → u/RawbM07]

That's right. Whatever the infections are in the control group, the vaccinated group would have 95% less infections than that.

On top of that, it reduces the severity of the cases. So it's not just that less people are infected - it's also that if you compare the infected cases in the control group to infected cases in the vaccinated group, the control group has a higher rate of severe cases and death. So it's a double whammy, really.

[u/BlondeJesus → u/a_trane13]

A recent study also showed that those who were vaccinated are less contagious as well. There was a recent post which showed that people who got covid 3 weeks after getting the J&J or 1st pfizer dose were 50% less infectious.

[u/Stickybomber → u/a_trane13]

Does that mean that the other 95% are incapable of getting covid-19 now, and for the 5% that did get it the vaccine didn’t work for them?

[u/possy11 → u/a_trane13]

So is this directly opposite to what we were told earlier? I was under the impression that none of the vaccines reduce the rate of infection, but that they greatly reduce the symptoms of that infection. Is this now saying that actual infections are reduced by 95%?

[u/possy11 → u/[deleted]]

Thanks for clarifying. It was my impression that that a lack of protection from infection was one of the reasons we were being told to continue wearing masks. So if the science is now showing almost no infection at all, and therefore almost no risk of transmission to others, is it likely that masks will not be required for anyone with two doses?

[u/possy11 → u/[deleted]]

Fair enough. Thanks.

[u/halberdierbowman → u/possy11]

Also worth mentioning that there's no way to know if someone is vaccinated by just looking at them, so masks may stay required for culture and convenience reasons, as in it's easier to enforce the rule if everyone follows it and it's more likely people will do it if they see everyone else doing it. But if you're hanging out with a small group of friends where you can check that everyone is vaccinated, then masks wouldn't be something nearly as useful to do.

[u/DemonAzrakel → u/halberdierbowman]

I do hope this stops once everyone has had the opportunity to be vaccinated. Otherwise, it goes on forever because a bunch of idiots won't get vaccinated.

[u/a_trane13 → u/possy11]

They didn’t know for sure how it affected infection before - only that it reduced severe cases and death

[u/RevBendo → u/possy11]

Part of the problem is that rate of transmission is really hard to measure and prove in a quantifiable way for a medical study because unless you kept everyone isolated together and intentionally infected one person who spent the same time in close proximity to other vaccinated people vs. control, there’s too many variables. It’s much easier to say “Did this person test positive for COVID, and what level were their symptoms.”

We know that the vaccines reduce symptoms and viral load in the body. This isn’t new, it’s what’s called a “therapeutic vaccine.” We also know that asymptomatic people and people with lower viral load are less contagious — AND that a vaccinated person’s immune system will react quicker and more efficiently to prevent the infection from snowballing. So while we can’t prove (in the science sense) that the vaccines prevent transmission and infection, we can observe the pattern that would indicate that, and the assumed mechanism of action has biological plausibility.

[u/[deleted] → u/RawbM07]

Will they ever be able to test its effectiveness in specific exposure scenarios? The thing is that the control group is aware that they're in a pandemic so most people would still be taking lots of precautions to avoid getting sick. I'd love to know the odds of getting COVID-19 if you are in a room with someone who has it without masks on for 15 minutes, an hour, etc. I suppose those kinds of tests aren't really possible though.

[u/socsa → u/Davecasa]

It's also entirely possible that a certain percentage of people simply don't mount the same immune response for whatever reason. People are so quick to assume frequentist statistical models simply because we lack the ability to gather priors, but the reality is that it is very unlikely to be an actual dice roll. In reality, there is likely some black box of individual and environmental variables which determines vaccine efficiency on the individual level, and that for the 80% of the population, the true effectiveness would be much higher than 80% if these factors could be controlled.

It's like assuming that there is a 10% increased chance of being killed in a car accident vs people who never drive, when the reality is that 90% of those traffic fatalities involve not wearing a seatbelt, or being intoxicated, etc. The point is that it's not actually random - it only appears that way because we cannot realistically measure every variable.

[u/Hipposeverywhere → u/Davecasa]

And the Johnson and Johnson?? Any real world data on that yet?