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British scientists are starting a study Thursday to find out if it’s OK to mix and match COVID-19 vaccines. The vaccines being rolled out now require two doses, and people are supposed to get two shots of the same kind, weeks apart. Guidelines in Britain and the U.S. say the vaccines aren’t interchangeable, but can be mixed if the same kind isn’t available for the second dose or if it’s not known what was given for the first shot. (Cheng, 2/4)

With the steady supply of vaccines always in question, the researchers said the information they collect would be useful not only for the UK but for the whole world. There is also the possibility that giving an individual two different vaccines in a row might give greater protection against the more infectious Covid variants that have emerged in the UK, South Africa and Brazil. (Boseley, 2/4)

Over 800 participants [are] expected to take part, the researchers said. That makes it much smaller than the clinical trials that have been used to determine efficacy of the vaccines individually. The trial will not assess the overall efficacy of the shot combinations, but researchers will measure antibody and T-cell responses, as well as monitor for any unexpected side effects. (2/3)

Mixing vaccines to create an enhanced immune response is common for inoculations targeting diseases such as hepatitis A and B. Combining shots can boost the immune response because the second shot won’t be limited by any immunity the body has built up to the platform delivering the first vaccine. Both the Astra and Pfizer shots target the spike protein that the virus uses to enter cells. The British drugmaker’s vaccine is carried by a weakened chimpanzee adenovirus, while the U.S. company’s shot uses genetic material called messenger RNA. (Ring, 2/4)