Memory B cells become more sophisticated over time, learning to recognize a diverse set of viral genetic sequences. The longer they have to practice, the greater the range of virus variants they can thwart.
Researchers showed last year that the elite school in the lymph nodes where the B cells train, called the germinal center, remains active for at least 15 weeks after the second dose of a Covid vaccine. In an updated study published in the journal Nature, the same team showed that six months after vaccination, memory B cells continue to mature and the antibodies they produce gain the ability to recognize new variants.
“Those antibodies at six months are better binders and more potent neutralizers than those produced one month after immunization,” said Ali Ellebedy, an immunologist at Washington University in St. Louis who led the study.
In the latest study, another team showed that a third injection creates an even richer pool of B cells than the second injection, and that the antibodies they produce recognize a wider range of variants. In lab experiments, these antibodies were able to repel the Beta, Delta, and Omicron variants. In fact, more than half of the antibodies seen a month after a third dose were able to neutralize Omicron, even though the vaccine was not designed for that variant, the study found.
“If you’ve had a third dose, you’ll have a rapid response that will be quite specific to Omicron, which explains why people who’ve had a third dose do so much better,” said Michel Nussenzweig, an immunologist at Rockefeller University. who led the study.
Memory cells produced after infection with the coronavirus, rather than by the vaccines, appear to be less potent against the Omicron variant, according to a study published last month in Nature Medicine. Immunity generated by infection “varies quite a bit, while the vaccine response is much more consistently good,” said Marcus Buggert, an immunologist at the Karolinska Institute in Sweden who led the study.
While most people, vaccinated or not, show only a small decrease in their T-cell response to Omicron, about one in five had a “significant reduction in their response” of about 60 percent, said Dr. buggers. The differences are most likely because of their underlying genetic makeup, he said.