Mixing Covid Vaccines Is Effective in Study on Pfizer, Astra

Mixing other vaccines with those from AstraZeneca Plc or Pfizer Inc. offers at least as effective protection against Covid-19 as giving two doses of the same shots, a U.K. study found.

The University of Oxford study, published Monday in the Lancet medical journal, tested vaccine combinations on more than 1,000 volunteers over 50. Some were immunized with a second dose from Moderna Inc. or Novavax Inc. nine weeks after having received a first shot of AstraZeneca or Pfizer.

Both Moderna and Novavax boosted immunity after the Astra vaccine, compared with a second Astra injection, while only Moderna increased antibodies after ...