Germany's vaccine committee has recommended anyone who received an AstraZeneca first dose have Pfizer or Moderna shots as the second for better protection against the coronavirus, including the Delta variant, tABC reports.

Studies show that the immune response is "clearly superior" when an AstraZeneca shot is combined with a second mRNA vaccine, compared with double AstraZeneca jabs, Germany's Standing Committee on Vaccination (STIKO) said.

Researchers at the UK's University of Oxford this week said they had found a combination of AstraZeneca followed by Pfizer proved to be nearly as potent as two Pfizer vaccines.

The commission recommended the mix "regardless of age" and with a minimum gap of four weeks between the two shots.

Several countries, including Canada, Spain, and South Korea, have already approved vaccine dose-mixing.