How can a cold protect against Covid-19?

Runny nose, sore throat, and sometimes headaches: cold symptoms are usually mild. It can be caused by a variety of different viruses, including coronaviruses. A new study, published in NatureCommunications and led by researchers at Imperial College London, shows that a cold infection could offer protection against Covid-19, thanks to the immune cells, called T cells, that it generates.

A trial on uninfected and unvaccinated people

Previous research has shown that T cells induced by other coronaviruses can recognize SARS-CoV-2. In this new work, the British researchers wondered how the presence of these T cells at the time of exposure to SARS-CoV-2 could influence a person’s infection. The authors started their work in September 2020, when most people in the UK had not been infected or vaccinated against the new coronavirus. They gathered a group of 52 people: all lived with a Covid-19 positive person, whose infection had been confirmed by PCR. Participants took PCR tests at the start of the study and then 4 and 7 days later to determine if they too had developed an infection. In parallel, blood samples were taken within 1 to 6 days of exposure to the virus. This allowed the researchers to analyze levels of pre-existing T cells, induced by colds brought on by common coronavirus infections. The researchers found that there were significantly higher levels of these T cells in the 26 people who were not infected, compared to the 26 people who were. “Although this is an important discovery, it is only a form of protection, and I want to emphasize that no one should rely on this alone, recalls Rhia Kundu, the lead author of the study. The best way to protect yourself against COVID-19 is to be fully vaccinated, including getting your booster dose.”

A unique mode of protection

“Being exposed to the SARS-CoV-2 virus does not always lead to infection, and we wanted to understand whysays Dr. Rhia Kundu. We have found that high levels of pre-existing T cells, created by the body when infected with other human coronaviruses such as the common cold, can protect against COVID-19 infection.” Especially since they offer a different protection from that provided by current vaccines: according to their conclusions, the T cells have targeted internal proteins of the virus, rather than the external spike protein, to protect themselves against infection. “The spike protein is under intense immune pressure from vaccine-induced antibodies that lead to the appearance of mutations that escape the vaccineadds study co-author Ajit Lalvani. In contrast, the internal proteins targeted by the protective T cells that we have identified mutate much less.” Thus, they could become a vaccine target, and allow the development of effective serums, whatever the variant.