A mixed vaccination of first AstraZeneca and then a Pfizer COVID-19 vaccine boosted neutralising antibody levels by six times compared with two AstraZeneca doses, research from South Korea shows.

The study involved 499 medical workers – 100 receiving mixed doses, 200 taking two doses of the Pfizer vaccine and the remainder getting two AstraZeneca inoculations.

The researchers also analysed neutralising activity against major variants of concern, the Korean Disease Control and Prevention Agency (KDCA) said.

None of the groups demonstrated reduced neutralising activity against the Alpha variant, first identified in Britain, but the neutralisation titre decreased by 2.5 to sixfold against Beta, Gamma and Delta, first detected in South Africa, Brazil and India respectively.