Israel rolled out almost entirely on Pfizer and they followed the same dosing schedule as the US did--3 weeks between shots. That was the quickest way to ramp up protection against infection.
The UK has highish vaccination rates, but they used AZ and Pfizer, mixed it sometimes, and also had a delayed dosing schedule. They've had a big case spike just like the US and Israel, but their hospitalization rates are remaining much lower. There's thoughts that the delayed second dose may provide for better long-term immunity, or just that their second doses were not as long ago as a lot of Israeli and US second doses, so their antibody levels are still high. A third dose in Israel in their 60+ population is seeing that group leveling off pretty clearly in recent weeks.
It's all still in the early investigative stages, but the main thought appears to be that Delta replicates and attaches so much better than OG sars-cov-2 that by the time your immune system spins up antibodies, the infection already has a foothold. So now you've got this rush of antibodies that's going to help fight off the infection more quickly and still reduce your odds of hospitalization quite a bit, but it's not going to stop the infection in its tracks and you'll still be able to spread. The vaccines were much more effective at preventing infections of non-Delta because those took a couple of days longer to really set in, giving your immune system more opportunity to build up antibodies.
We are still suppressing hospitalizations here and in Israel, but not nearly as much as the UK managed with this latest wave.
via NYT
https://t.co/zfpdYOlaYU