Antibodies produced by immune cells become steadily more formidable and precisely targeted against the SARS-CoV-2 virus for at least six months after COVID-19 vaccination, according to a study.
The researchers at Washington University School of Medicine in the US assessed the antibody response to the Pfizer-BioNTech vaccine in detail in people.
The findings, published on Tuesday in the journal Nature, suggest that declining antibody levels in the months after vaccination primarily represent a shift to a sustainable immune response.
The researchers also noted that even quite low levels of antibodies would continue to provide some protection against disease, as long as the virus does not change.
"If the virus did not change, most people who got two doses of this vaccine would be in very good shape," said senior study author Ali Ellebedy, an associate professor at Washington University.
"The antibody response we saw is exactly what we would expect from a robust immune response. We never thought that six months following that second injection, many people would still be actively improving the quality of their antibodies,” Ellebedy said.
The researchers collected blood from 42 participants and lymph node samples from 15 participants before each person received their first dose of the Pfizer COVID-19 vaccine and at weeks three, four, five, seven, 15 and 29 afterwards.
They also obtained bone marrow samples from 11 participants 29 and 40 weeks after the first vaccine dose.
Eight people provided all three kinds of samples, allowing the researchers to track the development of the antibody response over time within those individuals.
The researchers found that B cells, a family of immune cells that produce antibodies, targeted against SARS-CoV-2 persisted in the germinal centres of all participants for months.
Even six months after vaccination, 10 out of 15 people still had B cells in their germinal centers - boot camps where B cells are trained to make ever-better-quality antibodies.
The more time B cells spend in germinal centers, the more potent their antibodies get.
Germinal centers had been thought to last only a few weeks, so finding these boot camps still training B cells in a majority of people so long after vaccination was a surprise, Ellebedy said.
It indicates a strong antibody response that continued to mature and improve, he said.
Six months after vaccination, the antibodies were noticeably better than they had been in the beginning, they said.
In one set of experiments, the researchers found that only 20 per cent of early antibodies bound to a protein from the virus. Six months later, nearly 80 per cent of antibodies from the same individuals bound to the viral protein, they said.
"When you look at antibodies, quantity should not be your only concern.The antibodies at six months might be less in quantity, but they are much better in quality," Ellebedy said.
The researchers, however, noted that the quality of the antibodies is measured against the original virus that was used to design the vaccine.
If a new variant is different enough from the original, it may be able to escape once-powerful antibodies, they added.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
Covid-19 Cases Rising Again: WHO Issues Urgent Alert On Potentially Severe Variants Covid-19 Still Driving High Mortality Rate In This Country Biden Returns To White House After Exiting US Presidential Race Doctors Halt OPD Services Amid Nationwide Strike Over Kolkata Rape Horror Kolkata Rape-Murder: Fractures, 150 mg Semen, Other Claims Denied By Cops CBI Team At Kolkata Hospital For Digital Mapping Of Crime Scene Rs 700 Crore, 18,000 Women Workers: Foxconn's Tamil Nadu Housing Unit Global South Facing Challenges Of Food, Energy Security: PM Modi Centre Invites Bids To Empanel AI Infra Providers Under Rs 10,372 Crore Plan Track Latest News Live on NDTV.com and get news updates from India and around the world.