回复52楼::
The Pfizer and Moderna clinical trials were conducted in the US early on when covid prevalence was low and the UK variant hadn't yet emerged. So their % efficacy numbers came out in the 90's. Johnson&Johnson and AstraZeneca did their studies later when covid prevalence was higher and during the emergence of the UK strain, so their % was in the 70's and didn't look so good.
Moderna and Pfizer won't do another study because they're not going to get the numbers in the 90's given the currently high covid prevalence and various circulating strains.