This week, Thailand became the most recent country to announce a plan that will mix different COVID-19 vaccines. Multiple countries have begun offering mix-and-match vaccinations despite criticism from some health experts, reported The Washington Post.

  • Thailand, Indonesia and Canada are among the countries that have approved plans to mix vaccine doses, reported The New York Times.
  • Vietnam is also considering the possibility of mixing doses, per CNN.
  • The mix-and-match vaccination regimens include Oxford-AstraZeneca, Pfizer-BioNTech, Moderna and Sinovac vaccines, per CNN.

Clinical tests are underway regarding the effects of mixing vaccines, per The Washington Post.

What vaccines are countries planning to mix?

Different countries have approved different vaccine combinations, per The Washington Post. The combinations are varied and include a mixed two-dose vaccination regimen or a mixed three-dose vaccination regimen.

  • Thailand approved a plan to mix Chinese Sinovac vaccines with doses of AstraZeneca or Pfizer, per The New York Times.
  • According to the Thai government, people can receive these vaccines in any order, but the government recommends receiving a first dose of Sinovac then, three to four weeks later, a second dose of AstraZeneca or Pfizer.

For those who have already received two doses of Sinovac — such as the country’s health care workers — Thailand is recommending a third booster shot of AstraZeneca “right away,” per CNN.

  • Similarly in Indonesia, health care workers who received both doses of Sinovac can now receive a third booster shot of Moderna, per CNN.

In Canada, people can get the first dose of AstraZeneca and the second dose of Pfizer, per The Washington Post.

  • A few other European countries have also begun allowing recipients to receive mixed doses, per The Washington Post.
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Why are countries mixing vaccines?

All countries hope that mixing vaccines will boost people’s immunity to COVID-19, per The Washington Post.

  • Indonesia and Thailand approved of mixing vaccines partially due to concerns about the waning efficacy of Sinovac, reported The New York Times.
  • Chinese-made Sinovac vaccines have at least a 51% efficacy rate and have been approved by the World Health Organization. Questions have begun to grow about how well Sinovac protects against newer, more transmissible variants, such as the delta variant, per The New York Times.

Canada decided to allow mixed vaccines after findings that the AstraZeneca vaccine could potentially cause fatal blood clots in a small number of recipients, according to The Washington Post.

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Is it safe to mix vaccines?

Health experts have mixed opinions about whether or not it is safe to mix COVID-19 vaccines.

  • Health officials in Canada, Thailand and Indonesia have reaffirmed that their approved combinations of vaccines are safe and effective, per The New York Times.
  • An Ontario health minister said that their plan to mix vaccines is “based on studies from the (United Kingdom), Spain and Germany that have found mixing vaccines is safe and produces a strong immune response,” reported The Washington Post

WHO scientist Soumya Swaminathan said this week that mixing vaccines as booster shots is a “dangerous trend,” per The Washington Post.

  • This could lead to “a chaotic situation … if citizens start deciding when and who will be taking a second, a third and a fourth dose,” she said.
  • “We are in a bit of a data-free, evidence-free zone as far as ‘mix-and-match,’” she said.

Researchers in the U.S., Britain and Russia are currently conducting clinical trials about mixed vaccine regimens, per The Washington Post.

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