You’ve no doubt come across a situation where a whole household or workplace tests positive for COVID-19, but one person continually tests negative. This may happen for a whole bunch of different reasons, from their exposure to SARS-CoV-2 to the accuracy of the test, but one overlooked factor may be how their body previously coped with a common cold.
High levels of T cells — important white blood cells of the immune system — created by a previous infection of common cold coronaviruses appear to provide some protection against COVID-19, according to a new study published in the journal Nature Communications.
Scientists led by Imperial College London began their study in September 2020, when most people in the UK had neither been infected nor vaccinated against SARS-CoV-2. They took blood samples from 52 people who lived with someone who had a lab-confirmed SARS-CoV-2 infection in the past 6 days. The team then compared the levels of cross-reactive T cells found in the blood of the 26 people who did not become infected, compared to the 26 people who did. Their findings showed that people with higher levels of T cells, induced by previous common cold coronavirus infections, were less likely to test positive for COVID-19.
“Being exposed to the SARS-CoV-2 virus doesn’t always result in infection, and we’ve been keen to understand why. We found that high levels of pre-existing T cells, created by the body when infected with other human coronaviruses like the common cold, can protect against COVID-19 infection,” Dr Rhia Kundu, the first author of the study from Imperial’s National Heart & Lung Institute, said in a statement.
“While this is an important discovery, it is only one form of protection, and I would stress that no one should rely on this alone. Instead, the best way to protect yourself against COVID-19 is to be fully vaccinated, including getting your booster dose.”
The immune system is like a highly complex army, comprised of all different kinds of soldiers and weaponry that each serve their own purpose. T cells are just one of the units, a type of white blood cell that's specially trained to take on specific foreign particles. As this study shows, T cells can be versatile, responding to related viruses that share similarities in their structure.
Importantly, the T cells identified in the study provide protection by attacking proteins within the virus, rather than the spike protein on its outer surface. Since the “inner” part of the virus is less likely to mutate and change, this means the T cells could provide longer-lasting protection than other facets of the immune system, such as antibodies. This knowledge, the researchers say, could be a vital insight to keep in mind while developing the next generation of vaccines.
"The spike protein is under intense immune pressure from vaccine-induced antibody which drives evolution of vaccine escape mutants. In contrast, the internal proteins targeted by the protective T cells we identified mutate much less. Consequently, they are highly conserved between the various SARS-CoV-2 variants, including omicron,” explained Professor Ajit Lalvani, senior author of the study and Director of the NIHR Respiratory Infections Health Protection Research Unit at Imperial.
"New vaccines that include these conserved, internal proteins would therefore induce broadly protective T cell responses that should protect against current and future SARS-CoV-2 variants,” he continued.