Coronavirus Variants: T Cell Immunity Viable Even When Neutralising Antibodies Stumble

After over two years of its inception, the COVID-19 pandemic is still striking hard worldwide by emerging in different forms. Currently, Omicron has surfaced as the coronavirus variant of great concern as it appears to be extraordinarily spreading across populations. However, some initial studies have hinted that the new variant might cause less severe disease, and reports from many parts of the world suggest that the hospitalisation rate is lower than previous strains. Nevertheless, scientists and experts caution people to follow the covid-appropriate behaviours judiciously. 

The strategy to fight off the pandemic and the virus has been primarily concentrated on vaccination. In this process, one aspect of the immune system (the body's defence mechanism against foreign invaders) has got the most attention -- the antibodies. Protein molecules that belong to the immune system and kill pathogens (disease-causing agents like bacteria, viruses, fungi etc.) are called antibodies. Neutralising antibodies are the agents elicited by vaccines that let an infection not occur in the first place. Many studies have found that these neutralising antibodies can stumble to a great level, meaning they become lessened, and concomitantly, their effectiveness gets lowered. 

But, the situation might not be all discouraging. The immune system consists of various other ways to deal with a pathogen. One such arm of the immune system is the T cell immunity, and the evidence is growing, showing that the T cell immunity is still robust enough to recognise the Omicron variant and fight it off. 

The T cells are specialised cells belonging to the immune system. They perform the dual task of sending signals about the presence of a pathogen in the body to other parts of the immune system as well as killing the pathogen by targeting particular cells infected by it. T cells generated either by previous infection or vaccination can recognise the Omicron variant even when the neutralising antibodies fade away, new studies suggest.

Omicron has several mutations on its spike protein, which the virus uses to get glued to human cells and thus, enter it. Afterwards, it proliferates inside the cells and spreads the infection in the body. The known targets of the T cells are found to be present on the spike protein of the heavily mutated Omicron variant. 

There are studies that have analysed the status of the T cells taken from people who have either received a vaccine or got a previous bout of infection. These studies, like this, this and this one, have found that such T cells can respond well to Omicron. 

T cell responses have been found to correlate with increased protection against severe COVID-19 disease, both in animal models and clinical studies in people. Scientists believe that it is due to the T cells that some vaccines like Pfizer-BioNTech have shown to be effective in preventing disease severity among people infected by the Omicron virus. Notably, vaccines like the Pfizer-BioNTech and Janssen (Johnson & Johnson) do not have a high level of neutralising antibodies against Omicron. 

Scientists believe that even if the number of infections cannot be contained in the absence of a strong level of neutralising antibodies, the T cell immunity can still offer a robust defence against getting a severe disease and thus, reduce the rate of hospitalisation. The T cell immunity can also attract more importance with the possible emergence of new variants in the future.