Is Mixing Vaccines More Effective?

In this week's edition of the Covid Q&A, we look at mixing shots. In hopes of making this very confusing time just a little less so, each week Bloomberg Prognosis is picking one question sent in by readers and putting it to experts in the field. This week's question comes to us from Rogelio in Manila, who has already received the Sinovac vaccine. But as the Chinese-developed vaccine has come under scrutiny for its effectiveness, Rogelio wonders if he should get a different shot as well. Rogelio asks:

Can I take a Pfizer or Moderna shot after my Sinovac jabs?

We’ve addressed a version of this question before, but it’s worth revisiting. Last week, we published an article on drug-company executives seeking to boost their own immunity by mixing shots. But it’s more than just a trend among wealthy people.

“Mixing vaccine platforms —a method known as heterologous prime boost— has a long history in immunology as being far superior to multiple doses of the same vaccine,” says Ross Kedl, an immunologist at the University of Colorado Anschutz School of Medicine.

The gist is this: Different types of vaccines boost the immune system in different ways, so multiple vaccines provide broader coverage.

Early research has suggested that such an approach may be an effective strategy with Covid-19. A study of nearly 700 people in Spain showed that people who got a second dose of Pfizer’s vaccine after a first dose from AstraZeneca saw their neutralizing antibodies climb sevenfold—a far more robust immune response than in those who had two Astra doses. Another small trial suggested that mixing the two vaccines triggered antibody responses about four times higher than just two doses of Pfizer’s shot.