Thread by @dgurdasani1

Myth busting thread: Vaccines *do* reduce transmission- even with delta. Anyone who says otherwise (and I've seen many scientists say this recently to rationalise not vaccinating children!) is misinterpreting the evidence. Let me explain

There are two levels of protection against transmission:
1. Protection against infection (if you don't get infected you can't transmit)
2. Protection against transmission *if* breakthrough infection occurs

When many people say there isn't protection against transmission, they're talking about 2. - that is- if you get infected, you can still transmit delta efficiently. But that doesn't account for the fact that you are *less likely* to get infected in the first place.

REACT-1 data from England has shown ~60% protection against infection on average (this changes over time, and protection after 5 months or so may be markedly reduced), but there is substantial protection (even if not complete) for several months.
gov.uk/government/new…

Waning makes a difference, and the effectiveness of protection reduces over time with delta, but between 40-70% protection for several months is reasonably good protection in a pandemic where infection can spread over very short periods of time.

If you *do get infected* (the chance of which is reduced), then it seems there is little or no protection against transmission. Transmission can be similar among those who are vaccinated who have breakthrough infections, and those who are unvaccinated.

So vital for those who are vaccinated to take precautions- masking, getting tested, isolating if positive, because the transmission is efficient as this study shows. Thanks for @LongDesertTrain for correcting an earlier error I made reading the study.
thelancet.com/journals/lanin…

This study also shows that most cases with breakthrough infection were those 3-4 months out from vaccination, again highlighting the significant impact of waning immunity over time on reducing protection against infections. But boosters can massively increase this.

Recent work suggests boosters can boost immunity to give very high protection against infection as well as severe disease - of course we don't know how long this lasts, and it may well wane again over time, but even several months of high protection in a pandemic is important.

Also notable that protection from infection in the above study was ~35% - lower than REACT-1. Potentially several reasons for this. It's possible that household members of those infected were also likely on average a longer period post-vaccine (e.g. partners).

But potentially also lower protection with prolonged household contact than other types of contact. But even these levels of protection from infection would likely have significant impact at population level. We've seen lower infection rates overall among the vaccinated.

So, it's worth trying to separate out protection from infection & onward transmission *if* infection occurs.I worry that the overwhelming messaging that's being put out is that there is no protection from transmission, when there clearly is, even if it's not perfect, and wanes.

Also important to point out that boosting can reverse the waning - at least temporarily (we don't know how long currently) - it can substantially improve protection from infection, and severe disease. So please get your boosters if you are eligible. To protect yourself & others.

Just because protection isn't complete doesn't mean it's *no* protection. Remember, if you don't get infected, you can't transmit. It doesn't mean we don't need to use mitigations with vaccination, but that vaccines provide one layer of multiple layers of protection.

And yes, if you are vaccinated and get infected, you can transmit efficiently, so you do need to take precautions (isolation etc.) to protect the people around you. And although vaccines reduce infection risk, they don't eliminate it, so wear a mask. It'll protect you & others.

Just want to add that the same applies to protection from long COVID. Two layers: -protection against infection -protection against long COVID/long COVID severity/duration Vaccines definitely protect against 1. (potentially also some of 2.), so they provide significant protection

Sorry, deleted an earlier continuation of this thread due to an error. The rest of the thread is here:

https://twitter.com/dgurdasani1/status/1462542033784958989?s=20