Coronavirus: Mixing jabs may give greater immunity

Taking the AstraZeneca jab, then Pfizer vaccine may be not only safe and effective but even potentially beneficial.

Research indicates that combining the AstraZeneca (left) and Pfizer (right) vaccines could be more effective. Pictures: Supplied

Taking the AstraZeneca jab then Pfizer ten weeks later could give stronger immunity than sticking with the same vaccine for both doses, a German study suggests.

The experiment is one of the first to indicate that swapping vaccines may be not only safe and effective but even potentially beneficial. However, the research is still in its early days and much remains to be learnt about how various combinations work.

There has been much speculation that patients who receive two vaccines based on separate underlying technologies might acquire better protection against Covid-19.

This is because the vaccines elicit different forms of immune response from the body. There is some evidence from clinical trials on people that this trick works with diseases such as ebola.

Scientists have also had promising results in mice that were subsequently infected with coronavirus. Up to now, though, there has been only very limited data on whether it can help humans to fend off the illness.

The question is of particular interest in Germany, where two million people under the age of 60 were given the Oxford-AstraZeneca vaccine before concerns emerged over serious side-effects that affect 1 in 100,000 recipients.

This group were advised to take the Pfizer vaccine for their second dose, even though little was known about what consequences this might have.

The first results come from a study involving 340 healthcare workers at the Charite research hospitals in Berlin.

Half were each given two shots of the Pfizer vaccine, three weeks apart. The others were given an AstraZeneca jab then a Pfizer dose 70 days later.

The researchers, led by Leif Erik Sander, kept track of the effects by sending participants a questionnaire every two days in the week after each infection. They also took blood samples and looked at how well the different parts of the patients’ immune defences were responding to the vaccines.

Overall there were no unusual safety problems, although a previous study had suggested that people who switched from AstraZeneca to Pfizer were markedly more likely to develop mild symptoms such as chills, fatigue and muscle aches.

The immune responses to the two vaccine combinations were strikingly similar, but the results have yet to be formally reviewed by independent researchers or published in a scientific journal.

Sandra Ciesek, 43, professor of medical virology at Frankfurt University, tweeted: “In short, the immune response is very good, as we expected, and comparable to a homologous immunisation with an mRNA vaccine [two doses of Pfizer].”

The Times