Covid Live Updates: mRNA Vaccines May Offer Lasting Protection, Study Finds
“The Pfizer and Moderna shots’ effects could last for years, a detailed look at immune responses suggests. Some lawmakers are urging Biden to commute prison sentences for people released early because of the virus.
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A third dose of the AstraZeneca vaccine is found to boost immune response.
The vaccines made by Pfizer-BioNTech and Moderna set off a persistent immune reaction in the body that may protect against the coronavirus for years, scientists reported on Monday.
The findings add to growing evidence that most people immunized with the mRNA vaccines may not need boosters, so long as the virus and its variants do not evolve much beyond their current forms — which is not guaranteed. People who recovered from Covid-19 before being vaccinated may not need boosters even if the virus does make a significant transformation.
“It’s a good sign for how durable our immunity is from this vaccine,” said Ali Ellebedy, an immunologist at Washington University in St. Louis who led the study, which was published in the journal Nature.
The study did not consider the vaccine made by Johnson & Johnson, but Dr. Ellebedy said he expected the immune response to be less durable than that produced by mRNA vaccines.
Dr. Ellebedy and his colleagues reported last month that in people who had survived Covid-19, immune cells that recognize the virus remained in the bone marrow for at least eight months after infection. A study by another team indicated that so-called memory B cells continue to mature and strengthen for at least a year after infection.
Based on those findings, researchers suggested that immunity might last years, possibly a lifetime, in people who were infected and later vaccinated. But it was unclear whether vaccination alone might have a similarly long-lasting effect.
After an infection or a vaccination, a specialized structure called the germinal center forms in lymph nodes. This structure is an elite school of sorts for B cells.
The broader the range and the longer these cells have to practice, the more likely they are to be able to thwart variants of the virus that may emerge.
After infection with the coronavirus, the germinal center forms in the lungs. But after vaccination, the cells’ education takes place in lymph nodes in the armpits, within reach of researchers.
Dr. Ellebedy’s team found that 15 weeks after the first dose of vaccine, the germinal center was still highly active in all 14 of the participants, and that the number of memory cells that recognized the coronavirus had not declined.
“The fact that the reactions continued for almost four months after vaccination — that’s a very, very good sign,” Dr. Ellebedy said. Germinal centers typically peak one to two weeks after immunization, and then wane.
“Usually by four to six weeks, there’s not much left,” said Deepta Bhattacharya, an immunologist at the University of Arizona. But germinal centers stimulated by the mRNA vaccines are “still going, months into it, and not a lot of decline in most people.”
Dr. Bhattacharya noted that most of what scientists know about the persistence of germinal centers is based on animal research. The new study is the first to show what happens in people after vaccination.
The results suggest that a vast majority of vaccinated people will be protected over the long term — at least, against the existing variants. But older adults, people with weak immune systems and those who take drugs that suppress immunity may need boosters; people who survived Covid-19 and were later immunized may never need them at all.
Exactly how long the protection from mRNA vaccines will last is hard to predict. In the absence of variants that sidestep immunity, in theory immunity could last a lifetime, experts said. But the virus is clearly evolving.
A third dose of the Covid-19 vaccine developed by AstraZeneca and the University of Oxford generated a strong immune response in clinical trial volunteers, Oxford researchers reported on Monday.
The finding indicates that the AstraZeneca vaccine could be an option should third shots end up being needed, for example to extend immunity. To date, the vaccine has been given as two doses, typically between four and 12 weeks apart.
The new data, detailed in a preprint manuscript that has not yet been peer reviewed, came from 90 study volunteers in Britain who were among the earliest to receive the shots in a clinical trial last year. This past March, they were given a third dose, roughly 30 weeks after their second.
Laboratory analyses showed that the third dose increased levels of antibodies to the virus in the volunteers to a point higher than seen a month after their second dose — an encouraging sign that the third shot would be likely to bring greater protection if the effectiveness of two doses waned over time.
“We do have to be in a position where we could boost if it turned out that was necessary,” Prof. Andrew Pollard, an Oxford researcher who has led studies of the vaccine, said in a news conference on Monday. “I think we have encouraging data in this preprint to show that boosters could be used and would be effective at boosting the immune response.”
Scientists and policymakers do not yet know whether booster shots may be needed. Researchers are hopeful that the protection conferred by the leading vaccines will last at least a year, but there is not yet evidence to know for sure.
Emerging coronavirus variants could also accelerate the need for booster shots. If third shots are deemed necessary in the coming months, their availability could be severely limited, especially in poorer countries that are lacking enough supply to give first doses to their most vulnerable citizens.
Earlier this month, the National Institutes of Health announced that it has begun a new clinical trial of people fully vaccinated with any of the three authorized vaccines in the United States. The goal is test whether a booster shot of the vaccine made by Moderna will increase their antibodies against the virus. Initial results are expected later this summer.
The AstraZeneca vaccine has won authorization in 80 countries since last December but is not approved for use in the United States, which already more than enough doses of its three authorized vaccines to meet demand. The shot has been the backbone of the struggling Covax program to provide vaccines to poor countries, accounting for more than 88 percent of the doses shipped out to middle- and low-income nations through last week.
AstraZeneca announced on Sunday that the first volunteers had been vaccinated in a separate study assessing a new version of the vaccine designed to protect against the Beta variant of the virus first seen in South Africa. Some study results suggested that the original version of the AstraZeneca vaccine may not be effective against that variant. Professor Pollard said the study would compare the effects of a third dose of the original vaccine against those of boosting volunteers with the new Beta-targeted vaccine.”
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