I'm sorry, I still don't understand what 95% efficacy means!

[GreenBacon]

Does it mean
a. Everyone who gets covid will have their symptoms reduced by 95%.
b. The chance of catching covid at all is reduced by 95%. However the unlucky 5% will suffer the same symptoms as without the vaccine.
c. Something else

Thanks

Out of 100 people, 95 will not 'catch' covid in terms of becoming sick.

5 people will get sick if they catch it.

But will the sickness of the 5% be the same as if they never had the vaccine or will they be less sick?

Don't forget there's a difference between 'efficacy' and 'effectiveness'. It's a scientific distinction but important nonetheless.

Efficacy -- performance in lab/trial conditions, controlled circumstances
Effectiveness -- performance in real-world conditions

There are 95% fewer cases of people becoming ill with Covid in people who are vaccinated than in those who are not vaccinated. This is really high. Vaccines for some other diseases have an efficacy of only around 50 %.

Interesting point op. So, can the 5% still get very ill/die or do they get get a milder version than if they hadn't had the vaccine?

@GreenBacon

But will the sickness of the 5% be the same as if they never had the vaccine or will they be less sick?

Not sure for the Pfizer vaccine. For the AZ one they reported that all the trial subjects that were symptomatic did not have severe disease.

In the Oxford trial, even of those who did catch it, zero people had serious disease and needed hospital treatment.

Efficacy is calculated by:

(1 - the number of people in the placebo group who develop symptoms/the number of people who were vaccinated who develop symptoms) x 100%

So 95% efficacy means that there was a reduction of 95% reduction of new cases in the vaccinated group compared with the placebo group in the trial. Trials only involve a small number of people and some groups may have been excluded from the trial eg children, people with certain health conditions so it doesn't always mean that in the real world the results will be the same.

Efficacy doesn't directly tell you anything about the people who are vaccinated and then develop symptoms, whether they will have milder symptoms or not.