https://www.medrxiv.org/content/10.1101/2021.07.25.21261093v1.full.pdf
We have previously seen that those who get vaccinated after having had covid have very high antibody levels - about ten times more than those with vaccine alone.
This study found that those who had covid plus Pfizer vaccine were about 85% less likely to get a breakthrough covid infection (alpha and beta variants) compared to those who had Pfizer alone.
This has implications for the booster trials, since the antibody levels after booster are similar to those who had covid plus vaccine. It will be very interesting to see if the booster has similar results.
Strangely, they did not see this effect with Moderna, but it appears that they did not have many data points past the first 20 days, and Moderna gives higher antibody levels than Pfizer at the beginning. In those 20 days, the people with vaccine only were not seeing many breakthrough cases, so there was no difference between the two groups.