Thread by @profshanecrotty

1/ A third COVID-19 vaccine with efficacy! 3 for 3 in phase 3 vaccine clinical trials! Extraordinary successes for science.

statnews.com/2020/11/23/ast…

2/ The AZ Oxford COVID-19 interim efficacy results are 70% overall. That is substantially less than the Pfizer and Moderna vaccines, over short time periods.

3/ There was a small AZ Oxford substudy with a half-dose 1st immunization and an interim efficacy of 90%. That study is much smaller than other studies, and details were not provided (cases etc.), so I don’t make much of that number for now.

4/ Of note, the AZ Oxford vaccine (high dose) appeared less effective in an animal model (macaques) than the Pfizer and Moderna vaccines, indicating the animal model is a good one, consistent with the conclusions of many scientists.

5/ The improved outcome with the half-dose 1st immunization will need to hold up (more cases and data), before it can be fully scrutinized. But, simplest explanation is vector immunity is a bigger problem with the higher dose, blunting effectiveness of the booster immunization.

6/ Vector immunity = immune responses against the adenovector. Such responses are usually the majority of the response to a viral vector vaccine.