Despite preliminary data, certain countries are going ahead with mixing and matching mRNA and adenoviral vector COVID-19 vaccines, usually guided by supply constraints.

Germany has made an official recommendation to mix-and-match vaccines, encouraging people to get a dose of an mRNA vaccine after their AstraZeneca jab. Chancellor Angela Merkel had followed her initial AstraZeneca shot with a Moderna jab in June. Canada and Thailand have also started administering COVID-19 shots on a heterologous schedule. While the European Medicines Agency (EMA) and the European Centre for Disease Prevention and Control (ECDC) did not issue any specific recommendation, but they have promoted mix-and-match approach in a press release which stated that good scientific grounds exist to expect that this approach would be safe and effective when used in vaccination against COVID-19… (Medpage Today)