This small-ish study suggests Pfizer-BioNTech should be considered as a 3-dose vaccine, with no benefit of a 4th dose. If these results were to be confirmed, future 'variant-adapted' boosters may best be administered yearly, as for seasonal flu.https://t.co/uAVEUxxlqo

— Prof Francois Balloux (@BallouxFrancois) January 17, 2022