Some updated info on vaccines including some good news on immune persistence:
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.
The findings add to growing
evidence that most people immunized with the mRNA vaccines may not need
boosters, so 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 before being vaccinated may not need boosters
even if the virus does make a significant transformation.
“It’s
a good sign for how durable our immunity is from this vaccine,” said
Ali Ellebedy, an immunologist at Washington University in St. Louis who
led the study, which was published in the journal Nature.
The
study did not consider the 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 had
survived Covid-19, immune cells that recognize the virus remained 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 those findings, researchers suggested that immunity might last
years, possibly a lifetime, in people who were infected and later
vaccinated. But it was unclear whether vaccination alone might have a
similarly long-lasting effect.
After
an infection or a vaccination, a specialized structure called the
germinal center forms in lymph nodes. This structure is an elite school
of sorts for B cells.
The broader the
range and the longer these cells have to practice, the more likely they
are to be able to thwart variants of the virus that may emerge.
After
infection with the coronavirus, the germinal center forms in the lungs.
But after vaccination, the cells’ education takes place in lymph nodes
in the armpits, within reach of researchers.
Dr.
Ellebedy’s team found that 15 weeks after the first dose of vaccine,
the germinal center was still highly active in all 14 of the
participants, and that the number of memory cells that recognized the
coronavirus had not declined.
“The
fact that the reactions continued for almost four months after
vaccination — that’s a very, very good sign,” Dr. Ellebedy said.
Germinal centers typically peak one to two weeks after immunization, and
then wane.
“Usually by four to six
weeks, there’s not much left,” said Deepta Bhattacharya, an immunologist
at the University of Arizona. But germinal centers stimulated by the
mRNA vaccines are “still going, months into it, and not a lot of decline
in most people.”
Dr. Bhattacharya
noted that most of what scientists know about the persistence of
germinal centers is based on 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 variants.
But older adults, people with weak immune systems and those who take
drugs that suppress immunity may need boosters; people who survived
Covid-19 and were later immunized may never need them at all.
Exactly
how long the protection from mRNA vaccines will last is hard to
predict. In the absence of variants that sidestep immunity, in theory
immunity could last a lifetime, experts said. But the virus is clearly
evolving.
— Apoorva Mandavilli
