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A healthcare worker in Brazil prepares a COVID-19 vaccine shot. Andres Borges/Bloomberg via Getty Images
  • A new study has investigated whether T cells, which COVID-19 vaccines induce, recognize variants of the SARS-CoV-2 virus.
  • Alongside neutralizing antibodies and B cells, T cells play a crucial role in the immune response against disease.
  • The study results suggest that SARS-CoV-2 variants of concern — including Delta and Omicron — are effectively recognized by T cells in the body.

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Experts say that antibodies and T cells are both important in the body’s response against SARS-CoV-2, the virus responsible for COVID-19.

In the body, antibodies recognize and destroy viruses before they cause infection in cells, while T cells are responsible for destroying cells with a viral infection.

In a recent study, scientists discovered that COVID-19 vaccines prompt the body to make long lasting T cells that are effective against the SARS-CoV-2 virus and its variants.

The results suggest that T cells are key to limiting SARS-CoV-2 infection and may play a potential role in preventing severe diseases in the case of new variants.

The study appears in the journal Cell.

Co-study author Dr. Alba Grifoni, Ph.D., a scientist from the La Jolla Institute for Immunology, CA, explained the motivation behind the study to Medical News Today:

“We have been studying the role of immune responses (including neutralizing antibodies) and T cells in particular in SARS-CoV-2 since the beginning of the pandemic, first in infection, and then in the context of vaccination.”

“[SARS-CoV-2] variants are less susceptible to neutralizing antibodies, and vaccines have been relatively less effective in preventing infection from variants,” Dr. Grifoni explained, noting that vaccines are still “effective in preventing severe disease and hospitalization.”

“We wanted to see if variants in general and Omicron, in particular, were still effectively recognized by T cells,” she added.

“If this line of defense is still largely intact, it would fit with the fact that vaccines are still capable of preventing severe disease in the case of Omicron infections,” Dr. Grifoni concluded.

The new study included 96 participants who received vaccines that had approval for use in the United States.

These individuals received the Pfizer-BioNTech, Moderna, Johnson & Johnson, or Novavax vaccine.

The researchers collected blood samples from the participants at four time intervals to investigate how long T cells recognize SARS-CoV-2 variants. These intervals were as follows:

  • 2 weeks after the first dose
  • 2 weeks after the second dose
  • 3.5 months after the last dose
  • 5–6 months after the last dose

In addition, the experimenters also recruited individuals who were recovering following mild COVID-19. These participants served as the control group.

Finally, according to the availability of samples, the research team designed a cross-sectional study. In medical research, a cross-sectional study is a type of observational study where researchers collect data from many individuals at a given point in time.

The scientists observed that at 6 months post-vaccination, a large majority of T cell responses were still conserved against the Omicron variant.

Interestingly, they also noted that robust T cell responses remained the same, regardless of the vaccine administered or the variants encountered.

In contrast, the research team noticed a significant overall decrease in the activities of B cells and neutralizing antibodies across all SARS-CoV-2 variants.

These findings led the scientists to conclude that “the majority of the T cell responses may play an important role as a second-level defense against diverse variants.”

This point of view concurs with the authors of another paper that looked at T cell responses following SARS-CoV-2 infection and COVID-19 vaccination. They write that:

“T cell responses are a key armament against viral infections, which, in addition to assisting B cell activation for generating antibodies, help in providing protection from disease by eliminating virus-infected cells.”

“SARS-CoV-2 T cell responses induced by either natural infection or vaccines have been linked to rapid viral clearance and reduced disease severity, even when the neutralizing antibody response is reduced or absent.”

“Thus, if SARS-CoV-2 T cell responses hold up, they are likely to assist in limiting disease severity in infections caused by Omicron that seemingly escape neutralizing antibodies.”

A similar point of view is also shared by Prof. Eric Topol, the founder and director of the Scripps Research Translational Institute, CA.

As Prof. Topol explained on Substack, the main reason why Omicron has a lower rate of hospitalizations is not that the SARS-CoV-2 virus is less virulent, but rather because of the wall of immunity that the body has built up throughout the pandemic.

In a further commentary, he added that the body’s “last line of defense” is the T cell memory, which previous COVID-19 illness and vaccinations help create.

“[The T cell memory response] isn’t rapid, doesn’t protect against the initial infection in our upper airway, but, on-demand, kicks in to keep it there,” Prof. Topol says, pointing out that “this layer appears to be the main reason why Omicron appears mild.”

In a conversation with MNT, Dr. Grifoni reported several limitations of their research.

For instance, they explained that their study did not look at natural SARS-CoV-2 infection. As a result, the researchers do not know “how conserved T cell responses are in people [who had a natural infection] and had COVID-19 before and [now have an Omicron infection].”

In addition, Dr. Grifoni revealed that their sample size was limited to the San Diego areas in the U.S., therefore there is a bias in geographical location.

However, the study authors explained that they collaborated with other independent research groups and they all reached “the same conclusions on T cells and Omicron.”

Nonetheless, adhering to stipulated COVID-19 safety guidelines still remains important, such as getting booster doses of the vaccine.

As the study authors explain, “[Although] SARS-CoV-2 vaccines still give a response that helps in limiting disease severity, [this protection] is improved by getting a booster vaccination.”

All things considered, the study result provides a crucial foundation for future studies to build upon.