Britain Opens Door to Mix-and-Match Vaccinations, Worrying Experts – The New York Times

While decisions on alternative dosing regimens reside with health authorities, Pfizer believes it is critical health authorities conduct surveillance efforts on any alternative schedules implemented and to ensure each recipient is afforded the maximum possible protection, which means immunization with two doses of the vaccine, Mr. Danehy said.

With distribution of a coronavirus vaccine beginning in the U.S., here are answers to some questions you may be wondering about:

Both Pfizers and AstraZenecas vaccines introduce into the body a protein called spike that, while not infectious itself, can teach immune cells to recognize and fight off the actual coronavirus.

But the vaccines impart their immunological lessons through different methods, and do not contain equivalent ingredients. While Pfizers vaccine relies on a molecule called messenger RNA, or mRNA, packaged into greasy bubbles, AstraZenecas shots are designed around a virus shell that delivers DNA, a cousin of mRNA.

Both vaccines are intended to be doled out in two-shot regimens, delivered three or four weeks apart. While the first shots of each vaccine are thought to be somewhat effective at preventing Covid-19, its the second dose intended as a sort of molecular review session for the immune system that clinches the protective process.

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

Without evidence to back it, the hybrid vaccination approach seems premature, said Saad Omer, a vaccine expert at Yale University. Still, its not without precedent: Health authorities like the C.D.C. have previously said that if its impossible to give doses of a vaccine from the same manufacturer, providers should administer the vaccine that they have available to complete an injection schedule.

In a controversial move, the British government this week also decided to frontload its vaccine rollout, delivering as many first doses to people as possible a move that could delay second shots up to 12 weeks.

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Britain Opens Door to Mix-and-Match Vaccinations, Worrying Experts - The New York Times