Risk reduction - vaccines

[ikigai2021]

Hi, I've been reading around the vaccine information and I wondered if someone more scientifically literate might help interpret this study for me:

www.thelancet.com/journals/lanmic/article/PIIS2666-5247(21)00069-0/fulltext

Is it saying that the individual absolute risk reduction following vaccination is less than 2%?

It's saying that there are other metrics to judge vaccination efficacy that take account of accrual transmission likelihood, I.E. whether there's covid around or not, and the impact of public health measures like lockdownd. For the avoidance of doubt - currently there is covid around in the UK, it now looks like there always will be, and no we can't lockdown forever instead.

*actual not accrual

Thanks - I think I'm thicker than I thought, I can't make any sense of your reply

Could you use layman terms? I do appreciate it!

Does it mean that if rates were low then the individual absolute risk reduction following vaccination would be less than 2%?

Efficacy looks at relative risk between people in the trial, whereas they suggest taking into account everyone else in the population who had covid.

1. Not everyone in the community catches covid during the trial period, nor is everyone tested regularly and asymptomatically; so this overstates vaccine breakthrough cases and ignores the calculation that would be needed to take account of a vaccine protecting you for months or years longer while community cases increase.
2. Trials were conducted with lockdown or other restrictions (clubs / large events closed etc) and with people following social distancing, mask use and other health measures. That suppresses real community infection levels.

They're playing with numbers to be controversial, it's just a bit of silliness.

@ikigai2021

Does it mean that if rates were low then the individual absolute risk reduction following vaccination would be less than 2%?

Let me try an example. If you are in New Zealand, where your risk of catching covid is near zero due to border restrictions, then being vaccinated gives you minimal benefit due to the very low covid risk. So there the absolute risk would be minuscule; you would have to vaccinate tens of thousands at least to get the benefit of avoiding a single covid case. However, if New Zealand ever open the border that doesn't work any more, the absolute risk rises because the restrictions reduce. That's why absolute risk isn't helpful, because it doesn't actually tell you if the vaccine is useful when someone is exposed, which is what relative risk tells you.

*miniscule

Thank you! Ok, that's making more sense. Very interesting discussion though - I'm guessing absolute risk is related to individuals and relative risk more associated with population or public health

Yes, exactly. Your absolute risk of getting covid on a single trip to the pub is very low regardless of whether you've been vaccinated or not, because chances are nobody there has covid anyway. The risk gets bigger if you go every day for a few months, but it's still fairly low. Public health adds up tens of millions of people doing lots of low risk activities every day and get lots of infections.

Thank you so much for taking the time to explain this