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WHO Warns Against Mixing and Matching COVID-19 Vaccines

The World Health Organization has advised individuals against mixing and matching COVID-19 vaccines from different manufacturers.

In an online briefing, Soumya Swaminathan, “It’s a little bit of a dangerous trend here. It will be a chaotic situation in countries if citizens start deciding when and who will be taking a second, a third, and a fourth dose.”

“Individuals should not decide for themselves, public health agencies can be based on available data. Data from mix and match studies of different vaccines are awaited— immunogenicity and safety both need to be evaluated,” Swaminathan added.

The WHO’s Strategic Advisory Group of Experts on vaccines said in June the Pfizer vaccine could be used as a second dose after an initial dose of AstraZeneca if the latter is not available.

A clinical trial led by the University of Oxford in the UK is ongoing to investigate mixing the regimen of AstraZeneca and Pfizer vaccines. The trial was recently expanded to include the Moderna and Novavax vaccines.

Some studies are showing positive results from mixing vaccines, but these are in the preprint stage and need further studies to support them. Mixing vaccines is seen as an option in some countries where supply is short of one particular vaccine. But WHO is concerned about a situation where individuals decide for themselves which vaccines to get and how far apart to space them without guidance from health authorities.