Mix-and-match COVID vaccines trigger potent immune response

A news article in Nature describes a study led by the Carlos III Health Institute in Madrid that explored the benefits of combining different coronavirus vaccines. Preliminary results show that vaccinating people with both the Oxford–AstraZeneca and Pfizer–BioNTech COVID-19 vaccines produces a potent immune response against the virus SARS-CoV-2. The trial of more than 600 people — announced in an online presentation on 18 May — is the first to show the benefits of combining different coronavirus vaccines.

Because of safety concerns, several European countries are already recommending that some or all people who were given a first dose of the Oxford–AstraZeneca vaccine get another vaccine for their second dose. Researchers hope that such mix-and-match COVID-19 vaccination regimens will trigger stronger, more robust immune responses than will two doses of a single vaccine, while simplifying immunization efforts for countries facing fluctuating supplies of the various vaccines.

Arterial events, venous thromboembolism, thrombocytopenia, and bleeding after vaccination with Oxford-AstraZeneca in Denmark and Norway

A recent article in the BMJ describes a population based cohort study that assessed rates of cardiovascular and haemostatic events in the first 28 days after vaccination with the Oxford-AstraZeneca vaccine ChAdOx1-S in Denmark and Norway, and compared them with rates observed in the general populations.

The researchers observed increased rates of venous thromboembolic events, including cerebral venous thrombosis, among recipients of ChAdOx1-S. For the remaining safety outcomes, the researchers observed slightly higher rates of thrombocytopenia/coagulation disorders and bleeding, which could be influenced by increased surveillance of vaccine recipients. The absolute risks of venous thromboembolic events were, however, small, and the findings should be interpreted in the light of the proven beneficial effects of the vaccine, the context of any given country, and the limitations to the generalisability of the study findings.