On Jan. 24, 2022, the University of Oxford announced that a third booster dose of either the ChAdOx1 nCoV-19 (Oxford-AstraZeneca), BNT162b2 (Pfizer-BioNTech), AD26.COV2-S (Janssen) or CoronaVac (SinoVac) coronavirus vaccine induced a significant increase in antibody levels in those who have previously received two doses of CoronaVac.

The strongest responses were seen with mixed schedules, including against the Delta and Omicron variants of concern. The study results funded by the Ministry of Health, Brazil, and conducted by researchers from Brazil and the University of Oxford was published as a peer-reviewed paper in the Lancet.