Fever, sore throat and feverish state: when her 7.5-year-old son declared his first symptoms a few days ago, Laure immediately took him for an antigen test, which turned out to be positive. In the process, the young woman takes a test. It comes back negative. “But very soon I started having headaches and sore throats. And at D+2, my second test was positive. My husband, on the other hand, nothing. No symptoms, and a negative result”.
At home, the little family takes no particular precautions. “My colleague’s daughter-in-law caught him at school, and she and her partner isolated her in her room for a week, leaving her meals outside her door. Everyone does what they feel like, but my husband and I would never have imagined that we would stop any tender gesture towards our son. He continued to hug him, to dine at the table with us. And then we both got our third dose. My spouse took another test, still negative, and was surprised not to be contaminated. He’s had a lot of colds lately. And with each cold snap, he wondered if it was not the Covid-19 ”.
And if precisely, it was these small colds – in addition to the vaccine – which had had a protective effect? This is according to a study published this week in the scientific journal NatureCommunications by researchers at Imperial College London.
Cellular immunity stimulated by the common cold
“Being exposed to the SARS-CoV-2 virus does not always lead to infection, and we wanted to understand why,” says Dr Rhia Kundu, a fellow at Imperial College London’s National Heart and Lung Institute. and lead author of the study, in an interview broadcast by the prestigious university. To find out, the researchers launched their work in September 2020, when the population in the United Kingdom had been little contaminated and little vaccinated. They selected a sample of 52 people living with a person infected with Covid-19 (with confirmation by PCR test), therefore exposed to the virus. Each participant took three PCR tests (on D-Day, at D+4 and D+7), to detect any contamination. Result: 26 positive tests, 26 negative.
At the same time, blood samples were taken from them (on D-day, at D+7 and D+28), in order to determine their levels of pre-existing T cells. And those rates were significantly higher in the half spared the virus. “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,” confirms Dr Kundu . Clearly, for the researchers: the cold contracted by the participants who tested negative protected them from Covid-19.
A path forward for new vaccines
But for Dr Kundu, there is no question of recommending that people bet on the common cold to keep Covid-19 at bay. “While this is an important discovery, it is only a form of protection, and no one should rely on that alone. The best way to protect yourself against Covid-19 is to be fully vaccinated, and to receive your booster dose,” she insisted.
And this discovery could precisely make it possible to develop second-generation universal anti-Covid vaccines, which are more effective in protecting against new immune-escape variants, such as the Omicron strain. “Our study provides the clearest evidence to date that T cells induced by cold coronaviruses play a protective role against SARS-CoV-2 infection”, underlines Prof. Ajit Lalvani, co-author of the study and Director of the NIHR Respiratory Infection Health Protection Research Unit at Imperial College.
By what mechanisms could this immune memory, lodged in our T lymphocytes after a cold, give rise to new protective serums? “These T cells offer protection by attacking the internal proteins of the virus rather than the Spike protein, which is on its surface, according to Professor Lalvani. New vaccines including these internal proteins would therefore induce a T cell response, which should protect against current and future variants of SARS-CoV-2”.