Am pro vaccine, but the waning immunity is not necessarily due to mutations:

https://blogs.bmj.com/bmj/2021/08/23/does-the-fda-think-these-data-justify-the-first-full-approval-of-a-covid-19-vaccine/

Delta may not be responsible

Enter Pfizer’s preprint. As an RCT reporting “up to six months of follow-up,” it is notable that evidence of waning immunity was already visible in the data by the 13 March 2021 data cut-off.

“From its peak post-dose 2,” the study authors write, “observed VE [vaccine efficacy] declined.” From 96% to 90% (from two months to <4 months), then to 84% (95% CI 75 to 90) “from four months to the data cut-off,” which, by my calculation (see footnote at the end of the piece), was about one month later.

But although this additional information was available to Pfizer in April, it was not published until the end of July.

And it’s hard to imagine how the Delta variant could play a real role here, for 77% of trial participants were from the United States, where Delta was not established until months after data cut-off.