The World Health Organization's chief scientist on Monday advised against people mixing and matching COVID-19 vaccines from different manufacturers, calling it a "dangerous trend" since there is very little information on doing so.
"So it's a little bit of a dangerous trend here. We're in a data-free, evidence-free zone here as far as mix-and-match. There is limited data on mix and match. 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."
Dr. Soumya Swaminathan made her comments during the WHO's latest online briefing.
Infectious disease experts are weighing whether people who received Johnson & Johnson's single-dose vaccine should receive a booster of the Pfizer or Moderna mRNA-based vaccine which are said to be more effective against the highly contagious Delta variant.
One of those who did mix and match, Dr. Angela Rasmussen, a researcher at the University of Saskatchewan's Vaccine and Infectious Disease Organization, made headlines after she said on Twitter that she had gotten a dose of Pfizer's vaccine in June after receiving J&J's in April.
She also advised other J&J recipients, especially those living in areas with low vaccination rates, to talk to their doctors about doing the same.
Separately, Pfizer is pushing U.S. and European regulators to authorize a third booster shot to supplement its two-dose regimen. But health officials, including the WHO’s Swaminathan, have said there is no medical evidence that a third Pfizer shot is necessary.
"It has to be based on the science and the data, not on individual companies."
Instead of offering booster shots to highly-vaccinated, wealthy nations, the WHO’s director-general on Monday said companies like Pfizer should send those vaccines to the WHO to give to poorer countries whose unvaccinated citizens desperately need them against a Delta variant he described as "ripping around the world at a scorching pace."