Strange how the study found 2 doses barely effective but 3 were almost as good as natural immunity.
Effectiveness against symptomatic Omicron BA.1 infection was as follows (BNT162b2):
Previous infection without vaccination, 50.2%.
Two-dose vaccination without previous infection, 4.9% (i.e., negligible).
Three-dose vaccination without previous infection, 59.6%.
Two-dose vaccination with previous infection, 51.7%.
Three-dose vaccination with previous infection, 74.4%.
In all 5 groups:
Effectiveness was >90% against severe COVID-19, critical COVID-19, or death (collectively 0.3% of cases) caused by BA.1.
Altarawneh HN et al. Effects of previous infection and vaccination on symptomatic omicron infections N Engl J Med 2022 Jun 15; [e-pub]. (https://doi.org/10.1056/NEJMoa2203965. opens in new tab)
“Strange how the study found 2 doses barely effective but 3 were almost as good as natural immunity.”
I think it’s because immediately after getting a booster the immune system responds as if there’s an active infection and produces enough antibodies to fight that infection. To maintain that level, though, one would likely need boosters every few months.