Germany has issued a strong recommendation, probably the strongest in the world, for mixing of COVID-19 vaccines, based on efficacy.

The German Standing Committee on Vaccination (STIKO) has stated that individuals who receive a first dose of the Oxford-AstraZeneca vaccine should be given their second dose with an mRNA vaccine, irrespective of their age. Germany has become one of the first countries to strongly recommend that those who are administered a first dose of AstraZeneca COVID-19 vaccine, must be given either a Pfizer-BioNTech or Moderna vaccine for their second dose.

German Chancellor Angela Merkel herself received the Moderna vaccine as the second dose after she had received a first dose of the AstraZeneca vaccine. STIKO mentioned that latest study results suggest that mixed dose vaccination evoked a superior immune response… (CNN, July 2, 2021)