If one in 10 cold infections are from coronaviruses, then antibodies produced from these illnesses could surely give a bit more protection against COVID-19, right? A new study has just provided the answer to this question by showing that immunity induced by colds can indeed help fight off the far more dangerous novel coronavirus.

A study from Imperial College London that studied people exposed to SARS-CoV-2 or COVID-19 found that only half of the participants were infected, while the others tested negative. Before this, researchers took blood samples from all volunteers within days of exposure to determine the levels of an immune cell known as a T cell – cells programmed by previous infections to attack specific invaders.

Results show that participants who didn’t test positive had significantly higher levels of these cells; in other words, those who evaded infection had higher levels of T cells that attack the Covid virus internally to provide immunity — T cells that may have come from previous coronavirus infections (not SARS-CoV-2). These findings, published in the journal Nature Communications, may pave the way for a new type of vaccine to prevent infection from emerging variants, including Omicron.

Dr. Rhia Kundu, the first author of the paper from Imperial’s National Heart & Lung Institute, says: “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.” Despite this promising data, she warns: “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 common cold’s role in protecting you against Covid

The study followed 52 unvaccinated people living with someone who had a laboratory-confirmed case of COVID-19. Participants were tested seven days after being exposed to see if they had caught the disease from their housemates and to analyze their levels of pre-existing T cells. Tests indicated that the 26 people who tested negative for COVID-19 had significantly higher common cold T cells levels than the remainder of the people who tested positive. Remarkably, these cells targeted internal proteins within the SARS-CoV-2 virus, rather than the spike protein on its surface, providing ‘cross-reactive’ immunity between a cold and COVID-19.

Professor Ajit Lalvani, senior author of the study and Director of the NIHR Respiratory Infections Health Protection Research Unit at Imperial, explained:

“Our study provides the clearest evidence to date that T cells induced by common cold coronaviruses play a protective role against SARS-CoV-2 infection. These T cells provide protection by attacking proteins within the virus, rather than the spike protein on its surface.”

However, experts not involved in the study caution against presuming anyone who has previously had a cold caused by a coronavirus will not catch the novel coronavirus. They add that although the study provides valuable data regarding how the immune system fights this virus, it’s unlikely this type of illness has never infected any of the 150,000 people who’ve died of SARS-CoV-2 in the UK to date.

Other studies uncovering a similar link have also warned cross-reactive protection gained from colds only lasts a short period.

The road to longer-lasting vaccines

Current SARS-CoV-2 vaccines work by recognizing the spike protein on the virus’s outer shell: this, in turn, causes an immune reaction that stops it from attaching to cells and infecting them. However, this response wanes over time as the virus continues to mutate. Luckily, the jabs also trigger T cell immunity which lasts much longer, preventing the infection from worsening or hospitalization and death. But this immunity is also based on blocking the spike protein – therefore, it would be advantageous to have a vaccine that could attack other parts of the COVID virus.

Professor Lalvani surmises, “The spike protein is under intense immune pressure from vaccine-induced antibodies which drives the 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 SARS-CoV-2 variants, including Omicron.” He ends, “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.”