The study at hand compared thousands of folks in Israel who got the booster dose with those who didn’t. Everybody got the original Pfizer 2-shot vaccine at least six months previously. The study period included some months when the delta variant was dominant (about seven weeks starting in August 2021). Median follow-up of study participants was a surprisingly low 13 days.
Nevertheless, the booster seemed to reduce hospitalization, severe disease, and death from COVID-19.
See The Lancet for details.
Steve Novella has more details at Science-Based Medicine.
Steve Parker, M.D.