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Antibodies improve in quality for months after COVID-19 vaccination

A recent study conducted by researchers at Washington Saint Louis University School of Medicine has investigated the antibody response to the Pfizer-BioNTech vaccine. The experts found that antibodies produced by immune cells become steadily more formidable and more precisely targeted against the virus that causes COVID-19 for at least six months after vaccination.

Immunologists are familiar with the concept that antibody quality improves as antibody number decreases. In 1964, Washington University immunologists Dr. Herman Eisen and Dr. Gregory Siskind confirmed this phenomenon in rats. The current study is the first to follow the maturation of the antibody response in humans in great detail.

According to the research, decreased antibody levels in the months following vaccination are mostly due to a change to a more stable immune response. It takes a lot of energy to make a large number of antibodies. Because the immune system can no longer maintain such a high level of activity, it gradually changes to making lesser numbers of more effective antibodies.

The researchers explained that even very low levels of antibodies will provide some protection against sickness as long as the virus does not alter.

“If the virus didn’t change, most people who got two doses of this vaccine would be in very good shape. The antibody response we saw is exactly what we’d expect from a robust immune response,” explained study senior author Dr. Ali Ellebedy.

“We never thought that six months following that second injection, many people would still be actively improving the quality of their antibodies. To me, that is remarkable. The problem is that this virus keeps evolving and producing new variants. So, the antibodies are getting better at recognizing the original strain, but unfortunately the target keeps changing.”

The B cell family includes immune cells that generate antibodies. The B cell response involves maximum antibody production to the development of memory cells that may quickly churn out new antibodies the next time the body meets the same virus. 

To follow the complex response of B cells, samples must be collected from difficult-to-reach areas of the body. Key members of the B cell family can be found in the blood, lymph nodes, and bone marrow at various phases of the process. Obtaining B cells from lymph nodes requires the use of ultrasonography to find microscopic immunological structures known as germinal centres within the lymph nodes. The samples are extracted by inserting a needle into the pelvic bone.

For the investigation, blood samples were collected from 42 participants and lymph node samples were collected from 15 participants. Samples were obtained before each individual received an initial dose of the Pfizer-BioNTech COVID-19 vaccine, and at various times over the following weeks. Bone marrow samples were also taken from 11 subjects 29 and 40 weeks after the first immunization dosage.

The researchers were able to trace the antibody response over time in eight participants who submitted all three types of samples. Because none of the eight had been infected with the COVID-19 virus, their antibody responses were solely attributable to vaccination. 

The experts discovered that anti-SARS-CoV-2 B cells remained in the germinal centers of all subjects for months. B cells were still present in the germinal centers of 10 out of 15 participants six months following vaccination. 

Germinal centers are similar to boot camps where B cells are taught how to create higher-quality antibodies. The longer B cells stay in germinal centers, the stronger their antibodies become. Because germinal centers were assumed to last only a few weeks, finding these boot camps continually training B cells in the majority of patients so long after vaccination was unexpected, according to Dr. Ellebedy, and an indicator of a strong antibody response that continued to grow and strengthen.

The antibodies were significantly better six months after immunization than they were at the start. Only 20 percent of early antibodies bonded to a viral protein in one set of testing, yet samples from the same individuals showed that nearly 80 percent of antibodies linked to viral proteins six months later.

“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. And that refinement of the antibody response happens on its own. You get your shot, maybe your arm hurts for a day, and then you forget about it. But six months later your germinal centres are still ongoing and your antibodies are still getting better and better.” explained Dr. Ellebedy.

“Everything changes when a new variant comes. You have to retrain your immune system. It’s like updating your anti-malware software to make sure it matches the newest computer viruses that are going around. It doesn’t mean the old software was bad. It just means it no longer completely matches the viruses it is going to encounter.” 

The study is published in the journal Nature.

By Ashikha Raoof, Staff Writer

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