How long do immune cells against COVID-19 last after vaccination?

A study conducted by researchers at Johns Hopkins Medicine, in the United States, provides evidence that CD4 + T lymphocytes, cells of the immune system also known as helper T cells, produced by people who received either of the two available messenger RNA (mRNA) vaccines ) for him COVID-19 they persist six months after vaccination at only slightly reduced levels.

The study, published in ‘Clinical Infectious Diseases’, also points out that they are at significantly higher levels than for those who are not vaccinated. The researchers also found that the T cells they studied from SARS-CoV-2, the virus that causes COVID-19. This variant, which is currently predominant in the United States, causes more infections and spreads faster than previous forms of the virus.

“Previous research has suggested that the humoral immune response, where the immune system circulates virus-neutralizing antibodies, may decrease six months after vaccination, while our study indicates that the, where the immune system directly attacks infected cells, it remains strong, ”says the study’s lead author, Joel Blankson, a professor of medicine at Johns Hopkins University School of Medicine.

“The persistence of these vaccine-induced T cells, together with the fact that they are active against the Delta variant, has important implications in guiding the development of the covid vaccine and determining the need for boosters in the future.” has added.

To arrive at these findings, Blankson and his colleagues obtained blood from 15 study participants (10 men and five women) at three times: before vaccination, between seven and 14 days after their second dose of Pfizer / BioNTech or Moderna vaccine. , and six months after vaccination. The median age of the participants was 41 years and none had evidence of prior SARS-CoV-2 infection.

CD4 + T lymphocytes are nicknamed helper T cells because they help another type of cell in the immune system, the B lymphocyte (B cell), respond to surface proteins (antigens) in viruses such as SARS-CoV-2. Activated by CD4 + T cells, immature B cells become plasma cells that produce antibodies to mark infected cells for removal from the body or memory cells that “remember” it for a faster response to future infections. Therefore, a CD4 + T cell response can serve as a measure of how well the immune system responds to a vaccine and produces humoral immunity.

In their study, Blankson and colleagues found that the number of helper T cells that recognize the SARS-CoV-2 spike proteins was extremely low before vaccination, with a median of 2.7 spot-forming units (SFU, whose level is a measure of T-cell frequency) per million peripheral blood mononuclear cells (PBMC, identified as any blood cell with a round nucleus, including lymphocytes).

Between 7 and 14 days after vaccination, the frequency of T cells increased to a median of 237 SFU per million PBMC. Six months after vaccination, the level dropped slightly to a median of 122 SFU per million PBMC, a frequency of T cells at

The researchers also analyzed six months after vaccination the ability of CD4 + T cells to recognize spike proteins on the delta variant of SARS-CoV-2. They found that the number of T cells that recognized the delta variant peak protein was not significantly different from that of T cells tuned to the protein of the original virus strain.

Although the study was limited due to the small number of participants, Blankson believes it points to areas that deserve further investigation. “Robust expansion of T cells in response to spike protein stimulation is certainly indicated, supporting the need for further studies to show that booster injections successfully increase the frequency of SARS-CoV-specific T cells. 2 circulating in the blood ”, points out.

Follow us on twitter: