A third booster dose of a Covid-19 vaccine made by either AstraZeneca, Pfizer-BioNTech or Johnson & Johnson increases antibody levels significantly in those who have previously received two doses of Sinovac's CoronaVac shot, a study has found.

The study found that CoronaVac received the strongest boost from a viral vector or RNA shot, including against the Delta and Omicron coronavirus variants, researchers from Brazil and Oxford University said on Monday.

China-based Sinovac's vaccine uses an inactivated...