Cold immunity may protect against Covid, study finds

The protective response generated by defense T cells after a common cold can prevent infection by the Sars-CoV-2 virus and, consequently, protect against Covid-19.

This is the main finding of a study carried out by researchers at Imperial College London and published last Monday (10) in the scientific journal Nature Communications.

The research included 52 participants who lived together with people who had a confirmed diagnosis of SARS-CoV-2 infection. Of these, 26 had a negative result in the RT-PCR test for the coronavirus, and the other half, a positive result.

The main objective of the study was to see if people with the negative result had defense cells in the body against the virus.

Individuals who were exposed to Sars-CoV-2 underwent RT-PCR-type examinations on the first day after exposure and then on the fourth and seventh days. Blood samples were taken between the first and sixth days after exposure to analyze the presence of T cells already in the body after an infection with a common cold virus.

In those people with a negative RT-PCR test result, a high level of active defense cells was identified, that is, there was a memory cross-protection from a previous exposure by a common cold virus and Sars-CoV-2, preventing infection of the latter.

This cellular immunity, the authors say, was generated primarily to attack parts of the coronavirus such as the nucleocapsid (nuclear) protein or the proteins of the so-called envelope, the membrane that surrounds the virus’s nucleic material.

In contrast, there was reduced cross-immunity against the Spike S protein (or spike, the structure used by the coronavirus to enter cells).

As many of the Covid-19 vaccines used around the world have focused on inducing antibodies against the S protein, the Imperial College study could bring new focus to the development of second- and third-generation vaccines, say the authors.

In addition, as the production of memory T cells was verified in the first days after exposure to the virus — measured by the amount of interferon-gamma and interleukins, substances secreted by cells of the immune system in the face of an infection —, this is a strong indication that these memory cells already existed in the body, not being a response to a direct contact with the coronavirus.

According to Rhia Kundu, first author of the study and researcher at the National Heart and Lung Institute at Imperial College London, the research shows that high levels of memory T cells generated after common colds can protect against Covid, but should not replace the defense generated after taking the vaccine.

“While this is an important finding, this is yet another form of protection, and should not be the only tool to prevent the disease. Instead, the best way to protect yourself against Covid-19 is to keep your vaccinations up to date, including receiving the booster dose”, he says.

Another important aspect of the research is that, despite being released only now, it was carried out in September 2020, a period in which vaccines against Covid-19 were not yet available in the world.

Several studies have already shown that, although vaccines may partially lose their effectiveness six to eight months after the second dose, this drop is related to antibody rates, but cellular immunity, such as the one studied in the Imperial College research, is expected to endure.

In addition, vaccines were developed to protect against a serious condition of the disease, which can lead to hospitalization and death from Covid, but not against infection.

New vaccines that seek to neutralize the virus at the body’s gateway, that is, through the upper airways, such as the mouth and nose, may be able to prevent infection by Sars-CoV-2.

For professor and director of the Research Unit on Protection and Health of Respiratory Infections at the National Institute for Health Research in the United Kingdom (NIHR), Ajit Lalvani, this is the first study to show evidence that immunity generated against common colds can play a key role in preventing Covid, which explains why in many couples one person is infected with Sars-CoV-2, while the other is not.

“These T cells protect the organism by attacking the proteins inside the virus, and not the S protein, which is always under constant selective pressure, as it is where many of the mutations of Sars-CoV-2 arose”, he explains, who is one of the authors of the article.

“In contrast, the core proteins are much more conserved. New vaccines that use these proteins as a target can thus induce a much longer-lasting cellular immunity against the virus and its variants”, he says.