Vaccines from US pharmaceutical companies Pfizer / BioNTech and Moderna create a stubborn reaction in the body that could protect against the coronavirus for years, scientists reported on Monday (28).
The results add to the growing evidence that most people immunized with mRNA (messenger RNA) vaccines may not need a boost as long as the virus and its variants do not evolve much beyond their current forms is 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 bodes well for the duration of our immunity to this vaccine,” said Ali Ellebedy, an immunologist at Washington University in St. Louis who led the study published in the journal Nature.
Janssen’s Covid-19 vaccine was not included in the study, but Ellebedy said she believes her immune response is less tenable than that of mRNA vaccines.
The immunologist and his colleagues reported last month that in people who survived Covid-19, immune cells that recognize the virus remain dormant in the bone marrow for at least eight months after infection. A study by another team showed that so-called memory B cells 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 then vaccinated could last for years, possibly a lifetime. However, it is not clear whether the vaccine alone can have such a long-lasting effect.
Ellebedy’s team tried to answer this question by examining the source of memory cells: the lymph nodes, where immune cells train to recognize and fight the virus.
After an infection or vaccination, a specialized structure forms in the lymph nodes, the germinal center. This structure is an elite school for B-cell types – a camp where they become increasingly sophisticated and learn to recognize a wide variety of viral genetic sequences.
The greater the range and the time these cells have to exercise, the more likely they are to be able to fight off any virus variants that may appear.
“Everyone is always focused on developing the virus. This 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 be protection against the evolution of the virus, which is really exciting.”
After a coronavirus infection, the germinal center forms in the lungs. But after the vaccination, cells are formed in the lymph nodes in the armpits that researchers can reach.
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. Of these 14, the team took lymph node samples three, four, five, seven and 15 weeks after the first dose.
The meticulous work makes this a “heroic study,” said Akiko Iwasaki, an immunologist at Yale. “This kind of careful analysis over time in humans is very difficult.”
Ellebedy’s team found that 15 weeks after the first dose of vaccination, the germinal center in the 14 participants was still highly active and the number of memory cells that recognized the coronavirus had not decreased.
“The fact that the reactions have lasted almost four months after the vaccination is a very, very good sign,” he said. Sprouting centers usually peak a week or two after vaccination and then go away.
“Usually there isn’t much left in four to six weeks,” said Deepta Bhattacharya, an immunologist at the University of Arizona. But the germinal centers stimulated by the mRNA vaccines “are still there months later, and in most people there isn’t much of a decline.”
Bhattacharya commented that most of what scientists know about the persistence of germinal centers is based on animal studies. The new study shows for the first time what happens to people after vaccination.
The results suggest that the vast majority of those vaccinated are protected in the long term – at least against existing variants of the coronavirus. But older adults, people with weak immune systems, or those taking immunosuppressive drugs may need a booster; People who survived Covid and then got vaccinated may not need it.
It is difficult to predict exactly how long the mRNA vaccine protection will last. If there aren’t variants that bypass immunity, experts say it could theoretically last a lifetime. But the virus is clearly evolving.
“Anything that actually requires a boost would be based on variants, not reduced immunity,” said Bhattacharya. “I don’t really see this happening.”
People infected with the coronavirus and then immunized had large spikes in their antibody levels, likely because their memory B cells – which produce antibodies – had many months to develop before vaccination.
The good news: a booster vaccine is likely to have the same effect on people who have been vaccinated as a previous infection, Ellebedy said. “If you give them another chance to get involved, they’ll have a massive response,” he said, referring to memory B cells.
In terms of boosting the immune system, vaccination is “probably better” than recovering from the actual infection, he said. Other studies have shown that the memory B-cell repertoire produced after vaccination is more diverse than that produced by infection, suggesting that vaccines protect against variants better than just natural immunity.
Ellebedy said the results also suggest these signs of sustained immune response may be caused by mRNA vaccines alone, as opposed to those made in more traditional ways.
But that’s an unfair comparison because Janssen’s vaccine, for example, is given in a single dose, Iwasaki said. “If she had a backup, she might get the same kind of reaction.”
Translated by Luiz Roberto M. Gonçalves