Britain Opts for Combine-and-Match Vaccinations, Confounding Specialists

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Britain Opts for Mix-and-Match Vaccinations, Confounding Experts

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

Both Pfizer’s and AstraZeneca’s 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.

Covid-19 Vaccines ›

Answers to Your Vaccine Questions

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

    • If I live in the U.S., when can I get the vaccine? While the exact order of vaccine recipients may vary by state, most will likely put medical workers and residents of long-term care facilities first. If you want to understand how this decision is getting made, this article will help.
    • When can I return to normal life after being vaccinated? Life will return to normal only when society as a whole gains enough protection against the coronavirus. Once countries authorize a vaccine, they’ll only be able to vaccinate a few percent of their citizens at most in the first couple months. The unvaccinated majority will still remain vulnerable to getting infected. A growing number of coronavirus vaccines are showing robust protection against becoming sick. But it’s also possible for people to spread the virus without even knowing they’re infected because they experience only mild symptoms or none at all. Scientists don’t yet know if the vaccines also block the transmission of the coronavirus. So for the time being, even vaccinated people will need to wear masks, avoid indoor crowds, and so on. Once enough people get vaccinated, it will become very difficult for the coronavirus to find vulnerable people to infect. Depending on how quickly we as a society achieve that goal, life might start approaching something like normal by the fall 2021.
    • If I’ve been vaccinated, do I still need to wear a mask? Yes, but not forever. Here’s why. The coronavirus vaccines are injected deep into the muscles and stimulate the immune system to produce antibodies. This appears to be enough protection to keep the vaccinated person from getting ill. But what’s not clear is whether it’s possible for the virus to bloom in the nose — and be sneezed or breathed out to infect others — even as antibodies elsewhere in the body have mobilized to prevent the vaccinated person from getting sick. The vaccine clinical trials were designed to determine whether vaccinated people are protected from illness — not to find out whether they could still spread the coronavirus. Based on studies of flu vaccine and even patients infected with Covid-19, researchers have reason to be hopeful that vaccinated people won’t spread the virus, but more research is needed. In the meantime, everyone — even vaccinated people — will need to think of themselves as possible silent spreaders and keep wearing a mask. Read more here.
    • Will it hurt? What are the side effects? The Pfizer and BioNTech vaccine is delivered as a shot in the arm, like other typical vaccines. The injection into your arm won’t feel different than any other vaccine, but the rate of short-lived side effects does appear higher than a flu shot. Tens of thousands of people have already received the vaccines, and none of them have reported any serious health problems. The side effects, which can resemble the symptoms of Covid-19, last about a day and appear more likely after the second dose. Early reports from vaccine trials suggest some people might need to take a day off from work because they feel lousy after receiving the second dose. In the Pfizer study, about half developed fatigue. Other side effects occurred in at least 25 to 33 percent of patients, sometimes more, including headaches, chills and muscle pain. While these experiences aren’t pleasant, they are a good sign that your own immune system is mounting a potent response to the vaccine that will provide long-lasting immunity.
    • Will mRNA vaccines change my genes? No. The vaccines from Moderna and Pfizer use a genetic molecule to prime the immune system. That molecule, known as mRNA, is eventually destroyed by the body. The mRNA is packaged in an oily bubble that can fuse to a cell, allowing the molecule to slip in. The cell uses the mRNA to make proteins from the coronavirus, which can stimulate the immune system. At any moment, each of our cells may contain hundreds of thousands of mRNA molecules, which they produce in order to make proteins of their own. Once those proteins are made, our cells then shred the mRNA with special enzymes. The mRNA molecules our cells make can only survive a matter of minutes. The mRNA in vaccines is engineered to withstand the cell’s enzymes a bit longer, so that the cells can make extra virus proteins and prompt a stronger immune response. But the mRNA can only last for a few days at most before they are destroyed.

But the vaccines impart their immunological lessons through different methods, and do not contain equivalent ingredients. While Pfizer’s vaccine relies on a molecule called messenger RNA, or mRNA, packaged into greasy bubbles, AstraZeneca’s 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, it’s the second dose — intended as a sort of molecular review session for the immune system — that clinches the protective process.

While it’s 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, it’s 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, it’s not without precedent: Health authorities like the C.D.C. have previously said that if it’s 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.

The speedy deployment might afford more people partial protection against the virus in the short term. But some experts, including Dr. Moore, worry that this, too, might be unwise, and could imperil vulnerable populations.

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