Infosalus.- Study explains why Pfizer and Moderna vaccines are so effective against severe COVID-19

A new study by researchers at the Washington University School of Medicine in St. Louis and St. Jude Children’s Research Hospital (United States) has shed light on the quality of the immune response triggered by mRNA vaccines. COVID-19.

The first two vaccines created with mRNA technology, the COVID-19 vaccines from Pfizer/BioNTech Y Modern, are possibly two of the vaccines against COVID-19 most effective developed to date. In clinical trials, both were more than 90 percent effective in preventing symptomatic infection.

Although infections have increased with the appearance of the delta and omicron variants, vaccines are still quite effective in preventing hospitalizations and deaths. The success of the new technology has prompted scientists to try to find out why mRNA vaccines are so effective and whether the protection they provide is likely to last as new variants emerge.

This new study, published in the journal ‘Cell‘the researchers recruited 15 volunteers who received two doses of the Pfizer vaccine three weeks apart. The volunteers underwent a germinal center removal procedure from their lymph nodes 21 days after the first dose, just before the second, and then on days 28, 35, 60, 110 and 200 after the initial dose. None of the volunteers had been infected with SARS-CoV-2 at the start of the study. The researchers obtained helper follicular T cells from the lymph nodes and analyzed them.

The work shows that Pfizer’s vaccine intensively and persistently activates a type of helper immune cell that helps antibody-producing cells create large amounts of increasingly powerful antibodies, and also fuels the development of some types of immune memory. .

Known as helper follicular T cells, these cells last up to six months after vaccination, helping the body make better and better antibodies. Once helper cells decline, long-lasting antibody-producing cells and memory B cells help provide protection against severe disease and death.

Furthermore, many of the follicular T helper cells are activated by a part of the virus that does not appear to pick up mutations, even in the highly mutated omicron variant. These findings help explain why the vaccine Pfizer it causes such high levels of neutralizing antibodies and suggests that vaccination can help many people continue to produce strong antibodies even when the virus changes.

“The longer the helper follicular T cells provide help, the better the antibodies and the more likely you are to have a good memory response. In this study, we found that these follicular T helper cell responses go on and on. What’s more, some of them respond to a part of the spike protein of the virus that has very little variation. With the variants, especially the delta and now the omicron, we have seen some progress in infections, but the vaccines have held up very well in terms of preventing severe illness and death. I think this strong follicular T response is part of the reason why mRNA vaccines are still so protective.”, explains one of those responsible for the study, Philip Mudd.

The first antibodies produced in response to infection or vaccination are usually not very good. B lymphocytes have to go through a kind of boot camp in the so-called germinal centers of the lymph nodes before they can produce really strong antibodies. Helper follicular T cells are the sergeants of these ‘boot camps’.

Helper cells instruct antibody-producing cells to make increasingly potent antibodies and encourage those with the best antibodies to multiply and, in some cases, to become long-lasting antibody-producing cells or B cells of memory. The longer the germ centers last, the better and stronger the antibody response.

Researchers are now studying what happens after a booster dose and whether changes in follicular helper T cells could explain why people with compromised immune systems, such as those infected with HIV, do not elicit a strong antibody response.