Thread by @profshanecrotty

I have no problem with boosters allowed at 8 months for people who want them.

Is there American data indicating waning immunity against Delta? No. Nothing substantial.

Is there uncertainty about protective efficacy against Delta COVID-19 at 6 months? Yes 🧵

The COVID vaccines are incredible--they have exceeded all expectations. But, Delta is tougher to stop. It is so transmissible. The original coronavirus wasn't that hard for the immune system to stop, and 2-doses of vaccine worked amazing.

2-dose gives overall good immune memory. New Moderna science paper on antibodies at 6 months. Our T cell data. Multiple memory B cell data. The COVID vaccines have worked incredibly well! Six month clinical trial efficacies of 91% and 93%.

And at this moment in the Delta pandemic, the US experience had been fewer than 5 percent of the people being hospitalized and dying are fully vaccinated. Outstanding efficacy against severe disease and death!

Could the protection be better and longer lasting, against Delta? Some Delta breakthrough infections are occurring, and a booster dose would prevent most of those, so yes, a booster will improve immunity. Is it NEEDED? Uncertain.

https://twitter.com/profshanecrotty/status/1428859547565780992

And the US experience so far has been that the vaccines are working great against Delta (though imperfect compared to how amazing they were against Alpha)

But there is uncertainly now about whether high levels of protection last, and so a “better safe than sorry” policy of having boosters available to people who want them is quite reasonable, from a science perspective. And making that decision now makes sense.

The uncertainty about waning immunity mostly comes from Israeli reports

scientificamerican.com/article/should…

But also some other studies. Including some evidence of waning in the UK.

https://twitter.com/profshanecrotty/status/1428785670110150657

While the Israeli data are frustrating in that they haven’t been published in a formal way (and I defer to epi experts), the waning efficacy reports are enough at this point to at least create uncertainty about the durability of immunity against Delta symptomatic COVID-19.

Protection against hospitalization has remained high, but non-hospitalized COVID can be plenty bad, and Long COVID is a real concern.

Having more data on reactogenicity to a 3rd dose would be of real value for safety. It sounds like there is now data in Israel in 1000s of people indicating reactogenicity is the same for the 3rd dose as the 2nd, which is acceptable.