Countries weigh ‘mix and match’ COVID-19 vaccines

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A growing number of countries are looking at switching to different COVID-19 vaccines for second doses or booster shots amid supply delays and safety concerns that have slowed their vaccination campaigns.

Several medical studies to test the efficacy of switching COVID-19 vaccines are under way.

The following are countries that are weighing, or have decided to adopt, such a solution:


* Bahrain said on June 4 that eligible candidates could receive a booster shot of the Pfizer/BioNTech or the Sinopharm vaccine, regardless of which shot they had initially taken.


* The country’s National Advisory Committee on Immunization said on June 1 that recipients of a first dose of AstraZeneca’s vaccine can choose to receive a different vaccine for their second dose. It added that vaccines from Pfizer and Moderna could be used interchangeably.


* Chinese researchers in April were testing the mixing of vaccine doses developed by CanSino Biologics and a unit of Chongqing Zhifei Biological Products , according to clinical trial registration data.


* Finland’s Institute of Health and Welfare said on April 14 recipients of a first dose of AstraZeneca’s vaccine who were younger than 65 might get a different shot for their second dose.


* France’s top health advisory body recommended in April that people under 55 inject with AstraZeneca first and should receive a second dose with a so-called messenger RNA vaccine, although dose-mixing has not yet been evaluated in trials.


* Norway said on April 23 it would offer those who have received a dose of the AstraZeneca vaccine an injection with an mRNA vaccine as their second dose.


* Russia may start trials on a COVID-19 vaccine combining its Sputnik V vaccine and various Chinese shots in Arab countries, the Interfax news agency quoted Russia’s RDIF sovereign wealth fund as saying on June 4.

The RDIF also said that no negative side-effects were found during clinical trials combining COVID-19 vaccine using the AstraZeneca and Sputnik V shots, Interfax reported.


* South Korea said on May 20 it would run a mix-and-match trial, combining AstraZeneca doses with those developed by Pfizer and other drugmakers.


* Health Minister Carolina Darias said on May 19 Spain would allow people under 60 who received an AstraZeneca shot first to get a second dose of either the AstraZeneca or Pfizer vaccine, after preliminary results of a study by the state-backed Carlos III Health Institute.


* Sweden’s health agency said on April 20 that people under 65 who have had one shot of AstraZeneca’s vaccine would be given a different vaccine for their second dose.


* The United Arab Emirates and Bahrain have made the Pfizer/BioNTech PFE.N, BNTX.O coronavirus vaccine available as a booster shot to those initially immunised with a vaccine developed by the China National Pharmaceutical Group (Sinopharm).

A representative of Mubadala Health, part of the state fund, said a different vaccine could be provided as a booster shot but this was at the recipient’s discretion and health professionals did not make recommendations.


* Novavax said on May 21 it would take part in a mix-and-match vaccine trial to test the use of an additional vaccine dose from a different producer as a booster. The trial will start in June in the United Kingdom.

* The first findings of an Oxford University-led study released on May 12 indicated that people who received Pfizer’s vaccine followed by a dose of AstraZeneca, or vice versa, were more likely to report mild or moderate common post-vaccination symptoms than if they received two doses of the same type


* The U.S. National Institutes of Health (NIH) said on June 1 that it had started a clinical trial on fully vaccinated adults to evaluate the safety and immunogenicity of a booster shot of a different vaccine.