Britain opts for mix-and-match vaccines, puzzling experts



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Representatives for Public Health England and AstraZeneca did not respond to requests for comment.

The vaccines from Pfizer and AstraZeneca introduce a protein into the body called a spike which, while not itself infectious, can teach immune cells to recognize and fight the actual coronavirus.

But vaccines teach their immunological lessons by different methods and do not contain equivalent ingredients. While Pfizer’s vaccine relies on a molecule called messenger RNA, or mRNA, packaged in fat bubbles, AstraZeneca injections are designed around a viral envelope that delivers DNA, a cousin of mRNA.

The two vaccines are intended for distribution in two dose schedules, given three or four weeks apart. While the first injections of each vaccine are considered effective enough to prevent Covid-19, it is the second dose – designed as a sort of molecular exam session for the immune system – that concludes the protection process.

While it’s possible that swapping one vaccine for another could still teach the body to recognize the coronavirus, it’s still a scientific gamble. With different ingredients in each vaccine, people may not benefit as much from a second vaccine. Mixing and matching could also make it more difficult to collect clear data on vaccine safety.

Without supporting evidence, the hybrid vaccination approach appears “premature,” said Saad Omer, a vaccine expert at Yale University. Still, this is not without precedent: Health authorities like the CDC have previously said that if it is not possible to give doses of a vaccine from the same manufacturer, “suppliers should administer whatever vaccine they have” to supplement. an injection schedule.

In a controversial move, the UK government also decided this week to kick off its vaccine rollout, delivering as many first doses to people as possible – a move that could delay second injections for up to 12 weeks.

The rapid rollout could offer more people partial protection from the virus in the short term. But some experts, including Dr Moore, fear that this is also reckless and could put vulnerable populations at risk.

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