On Aug. 10, the WHO also cautioned against the quick adoption of mixing vaccines in an interim statement. “While these studies are encouraging, they require cautious interpretation given the limited sample sizes and lack of follow up, especially related to safety data, and the uncertain relevance of immunological readouts in relation to clinical impact,” it said.

But if proven to be safe and beneficial, the ability to mix and match Covid-19 vaccines could have several other benefits.

Mixing the Moderna and Pfizer vaccines

Canada is among the first countries actively trying to manage its vaccine supply issues by allowing the mixing of vaccines. For starters, those in the country who had taken the Pfizer shot were asked to take Moderna’s mRNA vaccine for their second dose. This has helped Canada overcome a supply bottleneck that delayed 2.4 million doses of Pfizer in June.

Taking it even further, on June 17, the Canadian National Advisory Committee on Immunization recommended those who received the AstraZeneca first dose should preferably take either the Pfizer or Moderna mRNA vaccine for their second dose. This decision was taken in light of the rare clotting events reported with the AstraZeneca vaccine. Canadian prime minister Justin Trudeau, too, took Moderna as his second dose on July 2 after the AstraZeneca first dose.

For countries in Asia and Africa, especially those heavily dependant on Covax and international vaccine donations, mixing vaccines could potentially ease the delay in supplies. Countries have currently been hit because of a low supply of the AstraZeneca vaccine, with many manufacturers including the Serum Institute of India running behind on their delivery timelines.

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