Pfizer-BioNTech and Moderna’s vaccines create a sustained immune response in the body that can protect against the coronavirus for years, a group of scientists reported Monday.
The results add to growing evidence that most people immunized with mRNA vaccines may not need a booster dose as long as the virus and its variants do not progress much beyond their current forms, which is not guaranteed. People who have recovered from COVID-19 before vaccination may not need a booster vaccination, even if the virus goes through a significant transformation.
“It’s a good sign of how persistent our immunity is to this vaccine,” said Ali Ellebedy, an immunologist at Washington University in Saint Louis, who led the study, which was published in the journal Nature.
The study did not include the vaccine manufactured by Johnson & Johnson, but Dr. Ellebedy said he expected the immune response to be less persistent than that of messenger RNA vaccines.
Ellebedy and colleagues reported last month that in those who survive COVID-19, immune cells that recognize the virus remain inactive (dormant) in the bone marrow for at least eight months after infection. A study by another team showed that so-called memory B cells continue to mature and strengthen for at least a year after infection.
Based on these results, the researchers suggested that immunity in people infected with the coronavirus and later vaccinated could last for years, and perhaps a lifetime. However, it was not entirely clear whether such a long-term effect could be achieved with vaccination alone.
Ellebedy’s team wanted to answer this question by studying the source of memory cells: the lymph nodes, where immune cells are trained to recognize and fight the virus.
After an infection or vaccination, a specialized structure called the germinal center forms in the lymph nodes. This structure is a kind of elite school for B cells, a training ground where they become increasingly sophisticated and learn to recognize a multitude of viral genetic sequences.
These cells are more likely to thwart emerging virus variants if they have more time and range to practice.
“Everyone is always focused on the development of the virus; it shows that the B cells are doing the same thing, ”said Marion Pepper, an immunologist at the University of Washington in Seattle. “And it will protect against the continued development of the virus, which is really encouraging.”
After infection with the coronavirus, the germinal center is formed in the lungs. But after the vaccination, the cells are formed in the armpit lymph nodes, within reach of the researchers.
Ellebedy and her colleagues recruited 41 people, including eight with a history of viral infection, who were immunized with two doses of the Pfizer BioNTech vaccine. The team collected lymph node samples from 14 of these people three, four, five, seven and 15 weeks after the first dose.
This careful work makes this a “heroic study,” said Akiko Iwasaki, a Yale immunologist. “This kind of careful time series analysis in humans is very difficult.”
Ellebedy’s team found that 15 weeks after receiving the first dose of the vaccine, the germinal center in all 14 participants was still highly active and the number of memory cells that can recognize the coronavirus had not decreased.
“The fact that the reactions have lasted almost four months after the vaccination is a very, very good sign,” said Ellebedy. Germ centers are usually highest one to two weeks after immunization and then decrease.
“Usually there isn’t much left after four to six weeks,” says Deepta Bhattacharya, an immunologist at the University of Arizona. But the germinal centers stimulated by the mRNA vaccines “remain active for months and do not decrease significantly in most people”.
Bhattacharya noted that most of what scientists know about the persistence of germinal centers comes from animal research. The new study shows for the first time what happens to people after vaccination.
The results suggest that a large majority of those vaccinated are at least protected against existing coronavirus variants in the long term. But older adults, people with weak immune systems, and those taking immunosuppressive drugs may need boosters; People who survived COVID-19 and were later vaccinated may never need it.
It is difficult to predict how long the protection of messenger RNA vaccines will last. If there weren’t any variants that bypass immunity, it could theoretically last a lifetime. But the virus is clearly evolving.
“Any need for a refresher would be due to variance, not a decrease in immunity,” said Bhattacharya. “I don’t see that happening.”
People infected with the coronavirus and then immunized experience significant increases in their antibody levels, likely because their memory B cells, which produce antibodies, took many months to develop before vaccination.
The good news: the booster will likely have the same effect on people who have been vaccinated as a previous infection, Ellebedy said. “If you give them one more chance to participate, they will react en masse,” he said, referring to memory B cells.
When it comes to boosting the immune system, vaccination is “probably better” than recovering from the actual infection, he said. Other studies have shown that the repertoire of memory B cells produced after vaccination is more diverse than that produced by infection, suggesting that vaccines protect against variants better than natural immunity alone.
Ellebedy said the results also suggest signs of a sustained immune response generated by mRNA vaccines rather than more traditional ones like Johnson & Johnson’s.
But that’s an unfair comparison since the Johnson & Johnson vaccine is given in a single dose, Iwasaki said, “It’s likely that J&J would have a second dose that could produce the same type of response.”
Apoorva Mandavilli is a reporter for The Times, focusing on science and global health. In 2019 he won the Victor Cohn Award for Excellence in Medical Science Reporting. @apoorva_nyc
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