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.
These findings are consistent with growing evidence that people who have been immunized with mRNA vaccines will not require boosters as long as the virus does not evolve beyond its current form — which isn’t guaranteed. People who recovered from Covid-19 before being vaccinated may not need boosters even if the virus does make a significant transformation.
Ali Ellebedy from Washington University in St. Louis was the lead researcher of the study.
The study did not consider the coronavirus 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 survived Covid-19, immune cells that recognize the virus lie quiescent in the bone marrow for at least eight months after infection. Another study indicated that memory-B cells grow stronger and mature for at least one full year after infection.
According to these findings, researchers suggest that immunity may last years and possibly even lifetimes in those who have been infected by the coronavirus but were vaccinated. It was not clear if vaccination could have a similar long-lasting effect.
Dr. Ellebedy and his team attempted to answer this question by looking at the source memory cells: The lymph nodes. This is where immune cells train in fighting the virus to recognize it.
After an infection, or vaccination, the germinal centre forms in lymph nodes. This structure is a type of elite school for the B cells. They learn to recognize many different viruses and become more sophisticated.
The more diverse the practice area and the longer the cells have been practicing, the more likely they will be to defeat any new variants.
Marion Pepper, an immunologist at University of Washington, Seattle, said: “Everyone always concentrates on the virus evolution — this is showing how the B cells do the same thing.” “And it is going to protect against ongoing evolution, which really encourages.”
The germinal centre forms in the lungs after infection by the coronavirus. Researchers can reach the lymph nodes in the armpits to learn how the cells are educated after vaccination.
Dr. Ellebedy and his team recruited 41 people. Eight of these were previously infected. Two doses of the Pfizer BioNTech vaccine were administered to them. The team collected lymph nodes samples from 14 of the people. These were taken at three, four (five, seven, seven and 15 week intervals after the first dose.
That painstaking work makes this a “heroic study,” said Akiko Iwasaki, an immunologist at Yale. This type of time-course analysis is very difficult for humans.
Dr. Ellebedy’s research team discovered that, 15 weeks after receiving the first vaccine dose, the germinal centre was still active in all 14 participants. Furthermore, the number of memory cells capable of recognizing the coronavirus hadn’t decreased.
Dr. Ellebedy noted that the fact that these reactions have continued for almost four years after vaccination is a very good indicator. Most germinal centers peak within one to two week of immunization. They then begin to decline.
Deepta Bhattacharya an immunologist at Arizona said that “usually by four to six weeks there’s not much left.” The mRNA vaccines have stimulated germinal centers, which are still functioning, several months later. Most people don’t notice any decline.
Dr. Bhattacharya stated that the majority of scientific information about the persistence and function of germinal centres is based upon 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 coronavirus variants. The boosters may be necessary for people over 65, with weak immune system or who are taking drugs that suppress immunity. However, people who have survived Covid-19 could not need them.
Exactly how long the protection from mRNA vaccines will last is hard to predict. Experts believe immunity could last a lifetime in the absence of any variants that can bypass immunity. But the virus is clearly evolving.
Dr. Bhattacharya explained that anything that would need a booster would be variant-based and not based on waning immune system. “I just don’t see that happening.”
People who were infected with the coronavirus and then immunized see a major boost in their antibody levels, most likely because their memory B cells — which produce antibodies — had many months to evolve before vaccination.
The good news? A booster vaccine is likely to have the same effect in immunized patients as previous infections, Dr. Ellebedy explained. “If you give them another chance to engage, they will have a massive response,” he said, referring to memory B cells.
He said that vaccinations are “probably better” than trying to recover from an infection in order to boost the immune system. Studies have shown that vaccines are more effective than natural immunity in protecting against variants of infection.
Dr. Ellebedy said the results also suggested that these signs of persistent immune reaction might be caused by mRNA vaccines alone, as opposed to those made by more traditional means, like Johnson & Johnson’s.
However, this is an unfair comparison. The Johnson & Johnson vaccination is administered as a single dose. Dr. Iwasaki said that if there was a booster for the Johnson & Johnson vaccine, then it could induce the same response.