Sander and his colleagues looked at 340 health-care workers who had received either two doses of the Pfizer–BioNTech vaccine, or an initial shot of the Oxford–AstraZeneca vaccine followed by a dose of Pfizer–BioNTech. There was no head-to-head comparison with people who received two doses of the same vaccine, but the authors found that in laboratory tests, those who received the combination produced 37 times more SARS-CoV-2 neutralizing antibodies and 4 times more SARS-CoV-2-specific immune cells, called T cells, than did people who had just one dose of the Oxford–AstraZeneca jab.īy the end of June, more results had emerged showing a similar effect. The study found a strong immune response in people who were dosed with the vaccine developed by pharmaceutical company Pfizer, based in New York City, and biotechnology firm BioNTech in Mainz, Germany, 8–12 weeks after receiving a dose of the Oxford–AstraZeneca vaccine. In May, researchers at the Carlos III Health Institute in Madrid announced results 4 from the CombiVacS trial.
This left many people partially vaccinated, unless they switched to a different brand for their second dose.
The jab has been associated with rare instances of a blood-clotting condition known as thrombosis with thrombocytopaenia - and in March, some European countries decided to halt its use in some groups of people. Mix-and-match studies were prompted, in large part, by concerns over the safety of the vaccine developed by the University of Oxford and pharmaceutical company AstraZeneca in Cambridge, both in the United Kingdom. But at least 16 vaccines have been approved for use in one or more countries, and mix-and-match studies so far have been small, so more extensive trials and long-term monitoring for side effects are sorely needed. The results are also giving researchers confidence that combining other COVID-19 vaccines, that haven’t yet been tested together, might also work. People can now “feel a bit more comfortable” with the idea of mix-and-match, says immunologist Leif Erik Sander at Charité University Hospital in Berlin.
Mix-and-match COVID vaccines trigger potent immune response
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