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Scientists said Monday that vaccines made by Pfizer-BioNTech and Moderna triggered an ongoing immune response in the body that may protect against the coronavirus for years.
The findings add to mounting evidence that most people immunized with mRNA vaccines may not need boosters, as 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 prior to vaccination may not need boosters even if the virus makes a significant turnaround.
“It’s a good sign of how sustainable our immunity is from this vaccine,” said Ali Al Yabidi, an immunologist at Washington University in St. Louis who led the study, which is published in the journal Nature.
The study did not take into account a Johnson & Johnson coronavirus vaccine, but Dr Ellebedy said he expects the immune response to be less durable than that produced by mRNA vaccines.
Dr. Ellipedi and colleagues reported last month that in people who have survived Covid-19, immune cells that recognize the virus lie 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 these findings, the researchers suggested that immunity may last for years, possibly a lifetime, in people who have had coronavirus and were subsequently vaccinated. But it wasn’t clear whether vaccination alone might have a similarly long-term effect.
Dr. Ellipedi’s team sought to address this question by looking at the source of the memory cells: the lymph nodes, where immune cells train to recognize and fight the virus.
After infection or vaccination, a specialized structure called the germinal center forms in the lymph nodes. This construct is an elite school of B cell types – a training camp where you become more complex and learn to recognize a variety of viral genetic sequences.
The wider and longer the range of exercise these cells had, the more likely they were to thwart viral variants that might emerge.
“Everyone is always focused on the evolution of the virus — and it shows that B cells do the same thing,” said Marion Pepper, an immunologist at the University of Washington in Seattle. “And it will be protective against the continued evolution of the virus, which is really encouraging.”
After infection with the Corona virus, the germinal center forms in the lungs. But after vaccination, cells are cultured in the armpit lymph nodes, within the researchers’ reach.
updated
June 28, 2021 at 8:22 a.m. ET
Dr. Ellipedi and colleagues recruited 41 people – including eight with a history of the virus – who were immunized with two doses of the Pfizer-BioNTech vaccine. From 14 of these people, the team extracted samples from lymph nodes three, four, five, seven and 15 weeks after the first dose.
This painstaking work makes this a “heroic study,” said Akiko Iwasaki, an immunologist at Yale University. “It’s very difficult to do this kind of accurate time-track analysis in humans.”
Dr. Ellipedi’s team found that 15 weeks after the first dose of the vaccine, the germinal center was still highly active in all 14 participants, and that the number of memory cells that recognized the coronavirus did not decrease.
“The fact that the reactions lasted for about four months after the vaccination – that’s a very, very good sign,” said Dr. Al Yabidi. Typically, germinal centers reach their peak 1-2 weeks after vaccination, and then fade away.
“Usually within four to six weeks, there is not much left,” said Deepta Bhattacharya, an immunologist at the University of Arizona. But the germ centers stimulated by the mRNA vaccines “are still going on, months after they happen, and there’s not much deterioration in most people.”
Dr. Bhattacharya noted that most of what scientists know about the continued existence of microbial centers is based on animal research. The new study is the first to show what happens in people after vaccination.
The results suggest that the vast majority of people who have been vaccinated will be protected in the long term — at least, from current variants of the coronavirus. But the elderly, people with weakened immune systems and those who take medications that suppress the immune system may need boosters. People who have survived Covid-19 and are subsequently vaccinated may not need it at all.
It is difficult to predict exactly how long protection from mRNA vaccines will take. Experts said that in the absence of variants that avoid immunity, it is theoretically possible for immunity to last a lifetime. But it is clear that the virus is evolving.
“Anything that requires a booster action will be variant based, not dependent on weakened immunity,” said Dr. Bhattacharya. “I just don’t expect that to happen.”
People who were infected with the coronavirus and then vaccinated see a significant increase in their antibody levels, likely because their memory B cells — which produce antibodies — had several months to develop before vaccination.
The good news: The booster vaccine will likely have the same effect as previous infections in immunized people, said Dr. Ellipedi. “If you give them another chance to engage, they’ll have a massive response,” he said, referring to memory B cells.
In terms of strengthening the immune system, he said, vaccination is “probably better” than recovering from an actual infection. Other studies have suggested that the stores of memory B cells produced after vaccination are more diverse than those from infection, suggesting that vaccines would better protect against variants than natural immunity alone.
The findings also suggest that these signs of a persistent immune reaction may be caused by mRNA vaccines alone, as opposed to those made by more traditional means, such as Johnson and Johnson, Dr. Ellipedi said.
But that’s an unfair comparison, because the Johnson & Johnson vaccine is given as a single dose, as Dr. Iwasaki said: “If J&J had a booster, it would probably trigger the same kind of response.”
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