People with immunity to original COVID-19 strain likely have some protection against Omicron: study

A new study has found that those who gained immunity to the original strain of SARS-CoV-2, the virus that causes COVID-19, likely have some protection against the Omicron variant.

The study, conducted by an international research team from Johns Hopkins Medicine, reports that people who have been vaccinated or exposed to infection have some level of protection against Omicron, since its mutations are not found in the parts of the virus that incite a cellular immune response.

However, researchers caution their finding only relates to one type of cellular immune response. Because of this, they say it may be the antibody-related immune response that fails when Omicron causes breakthrough infections.

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The findings were published earlier this month in mBio, a peer-reviewed scientific journal from the American Society for Microbiology. The research was done in collaboration with the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and ImmunoScape, a U.S.-Singapore biotechnology company.

Researchers say the study reinforces other findings out of the United States and South Africa that have shown similar results for people previously infected by or vaccinated against the original strain of COVID-19.

Scientist and study lead author Andrew Redd said researchers found in a January 2021 study that specific epitopes, or portions of a protein that elicit an immune response from the virus, are recognized by immune system cells called CD8+ T lymphocytes, also known as killer T-cells or cytotoxic T-cells, in those previously infected with the original COVID-19 strain.

Redd explained in a press release that this recognition enables a "cell-mediated attack on COVID" in an effort to eliminate the virus from the body.

"In our latest work, we found that these epitopes remained virtually untouched by the mutations found in the Omicron variant. Therefore, the CD8+ T cell response to Omicron should be virtually as strong as it was to the initial form of SARS-CoV-2," Redd said.

According to researchers, the T-cells used in the latest study were from convalescent blood samples collected in 2020 from 30 American patients who had recovered from mild to moderate cases of COVID-19. These samples were taken between 26 to 62 days after the donors stopped having COVID-19 symptoms to ensure their immune response to the virus was "fully mature," according to the study.

They were then analyzed to identify which T cells had responded to the virus.

In the January 2021 analysis, the blood samples were tested with 408 different SARS-CoV-2 epitopes from spikes on the virus surface, the virus capsule and non-structural proteins inside the virus, according to the study.

After analysis, researchers found that T cells from the convalescent donors were able to recognize 52 of the 408 epitopes.

In the latest study, researchers re-examined these 52 previously identified epitopes to see if they had been altered by "escape mutations," which are genetic changes that can enable a virus to avoid being susceptible to cell-mediated immunity.

Researchers noted the blood samples were properly stored between each study period.

Redd said in the release that researchers only found "one low-prevalence epitope from the Omicron spike protein that had a minor change" compared to the original strain of the virus.

"Overall, the Omicron variant is known to have some 50-plus mutational differences between it and the original SARS-CoV-2 strain, but it seems the virus has not evolved the ability to avoid T cell recognition," Redd said.

While the findings suggest immunity is maintained from the original COVID-19 strain through its subsequent variants, the study's authors say more research is needed to fully define why people who have this protection may still get sick from Omicron.