Thank you for your comment. I have heard of Virology Blog before, but I’ve just subscribed to its email newsletters now. The professor raised a good point about T-cells preventing severe diseases. The Pfizer mRNA vaccine also stimulates T-cells, which may explain its higher efficacy at preventing severe diseases (~97%) than preventing infection (~75%) by the B.1.351 variant.

https://www.nejm.org/doi/10.1056/NEJMc2104974