Mixing Astra and Pfizer shots creates strong immune response

Mixing doses of Covid-19 vaccines from Pfizer Inc. and AstraZeneca Plc creates a strong immune response, according to results from a University of Oxford study, a finding that could enable greater flexibility in the use of scarce supplies.

A mixed schedule of the Pfizer shot followed by the Astra vaccine, and vice versa, resulted in high concentrations of antibodies against Covid-19 when given four weeks apart, researchers reported Monday in the Lancet medical journal. Doctors and public health officials have been analyzing various ways to extend vaccine supplies -- by delaying the time between first and second doses, for example -- as many low- and middle-income nations try to figure out how to cope with vaccine scarcity. The ability to mix doses might help countries with supplies of different vaccines assist one another.