Is it safe to delay the second COVID vaccination?

Vaccine shortages and delayed distribution are hampering efforts to curb the SARS-CoV-2 pandemic. Therefore, some scientists have proposed to postpone the second dose of the double dose vaccine so that people can get the first dose. The initial recommended interval was 21 days for Pfizer vaccine and 28 days for Modelnashot. The two are currently licensed in the United States.Currently, the US Centers for Disease Control and Prevention Updated guidance The agency still advises individuals to stick to the initial schedule, but people say they can wait up to 42 days between doses. Also, developers of the AstraZeneca vaccine at Oxford University, which is licensed for use in the United Kingdom, suggest that even longer stretches are possible. Improved performance When the dose is at 12 week intervals. Their data is in a new preprint paper released prior to peer review. So what do you get? How long can you stay safe in a single shot? And what if the second shot isn’t available on time? Scientific American Explore the potential risks and benefits of delaying vaccination.

Why do you need 2 shots?
Vaccines are designed to produce immunological memory, which allows the immune system to recognize and dodge enemies that have invaded them, even if they have never encountered them before. Most COVID vaccines It elicits this response by presenting the immune system with a copy of the new coronavirus peaplomer that decorates its surface like a crown.

Two-shot vaccination aims for maximum benefit. The first dose stimulates immunological memory and the second dose hardens it, says Thomas Denny, Chief Operating Officer of the Duke Human Vaccine Institute. “It can be thought of as a gradient,” he adds. Single dose Pfizer The vaccine can reduce the risk of the average person with a symptomatological infection by about 50%, with a single vaccination. modern Shots can do so about 80%. Two doses of either vaccine reduce the risk by about 95%.

Why does the CDC allow up to 42 days between Pfizer and Modana vaccines?
CDC spokesman Kristen Nordlund updated the initial guidance after receiving feedback that some flexibility could help people, especially if they have a challenge returning to a particular day.The UK recommends dose stretching as a deliberate strategy for getting more first shots with more weapons, but the CDC proposes it as an option to do so. The schedule for the second shot is not that complicated. In the United States, vaccine deployment is painfully slow.About two months after the first injection was released to the public 3 percent Both populations are receiving both doses of the vaccine. And as vaccine producers struggle to keep up with demand, experts believe that some compromises are needed to ensure that people are fully vaccinated. “We need to use the resources we have to make the best decisions,” said Catherine Polling, a pediatrician at Wake Forest Baptist Health, a member of the CDC’s Immunization Implementation Advisory Board. I will. “If you have a lot of vaccines, you may take a different approach than if you had a limited vaccine, but you need a second dose.”

What kind of protection do you have until the 42nd day?
According to the data from Pfizer And modern In the study, the curve showing the number of infections in the unvaccinated group continued to swing upwards, whereas the curve in the vaccinated group did not swing upwards and was protected approximately 14 days after the first dose. Has started. With both vaccines, a single dose protected almost everyone from serious illness and, as mentioned above, was approximately 50% (Pfizer) or 80% (Moderna) effective in preventing COVID. Most study participants received a second vaccination on day 21 or 28, but some waited for day 42 or longer. However, the number of outliers is so small that no clear conclusion can be drawn about the implications of extending the two-shot regime. For example, of the 15,208 study participants vaccinated with the Moderna vaccine, only 81 (0.5%) were vaccinated outside the recommended period.

“At this point, there’s no best science to say that it’s 100% comfortable to boost after 35 or 40 days,” says Denny. “We respect public health concerns and have the belief that what we can do now is better than nothing.”

If people are only partially vaccinated with a single dose, can it fuel the more dangerous coronavirus mutants?
That is Real concernAccording to Paul Bieniasz, a retrovirus scholar at Rockefeller University. In the early days of the pandemic, no one’s immune system was ready for infection, and microorganisms were easily picked up, so there was little pressure to evolve a new coronavirus. But now millions of people have been infected and developed antibodies. Therefore, mutations that give the virus a way to circumvent these defenses It has become noticeable. “The virus evolves in response to antibodies, regardless of how the vaccine is given,” says Vienius. “The question is, will it accelerate its evolution by creating a national population of individuals with partial immunity?”

Just as antibiotic-resistant bacteria are fueled without completing the entire course of antibiotics, the body can become a breeding ground for antibody-resistant viruses if not fully vaccinated. However, Trevor Bedford, a computational biologist at the Fred Hutchinson Cancer Research Center, who is tracking viral mutations, said: Tweet The pace of evolution is not just determined by the weakness and strength of the immune system. It is also affected by the vast number of viruses that circulate in the population, he wrote. Without widespread vaccination, the amount of the latter, and the number of variants that can produce the more formidable virus, will continue to grow.

Does increasing the interval between the first and second doses increase the effectiveness of the COVID vaccine?
The result is possible. Not all COVID vaccines are made the same, and the optimal dosing schedule depends on the particular design. Some vaccines are based on fragile strips of genetic material known as mRNA, some rely on harder DNA, and others use protein fragments. These cores can be carried to cells covered with small lipid droplets or harmless chimpanzee virus.

Given that difference, Denny isn’t surprised that the DNA-based Oxford-AstraZeneca vaccine has been tested and found to be effective at 12-week intervals between shots. This is about 3-4 times longer than the recommended interval for mRNA-based Moderna and Pfizer vaccines. Over time, researchers may find that a slightly different dosing schedule than that tested in the first clinical trial is more effective. “We could have done a two-year dosing study, but that’s not the most responsible thing to do in a world like this,” says Denny. “Don’t make perfection a good enemy.”

The author would like to thank Rachel Lance for suggesting the sources contained in the story.

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