Is it allergies, a common cold, the flu or COVID-19? These are the questions individuals find themselves asking nowadays when they wake up with a runny nose and sore throat. Doctors recently confirmed it could actually be both the flu and COVID-19 simultaneously, a condition termed “flurona” that can wreak havoc on a person’s immune system.
Conversely, researchers have discovered a common cold does the opposite—it protects the immune system from SARS-CoV-2 infection.
“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,” said Rhia Kundu, a postdoctoral research associate at Imperial College London and first author of the new paper published in Nature Communications.
The small-scale study began in September 2020, when most people in the UK had neither been infected nor vaccinated against SARS-CoV-2. It included 52 participants who lived with someone with PCR-confirmed SARS-CoV-2 infection and had therefore been exposed to the virus. Ultimately, 26 people became infected with SARS-CoV-2, while 26 avoided the virus.
Blood samples were from taken from each participant within 1-6 days of exposure. This enabled Kundu and her team to analyze the levels of pre-existing T cells induced by previous common cold coronavirus infections that also cross-recognize proteins of the SARS-CoV-2 virus. They found that there were significantly higher levels of these cross-reactive T cells in the 26 people who did not become infected compared with the 26 people who did.
What’s even more interesting about these T cells is what they targeted. Rather than going after the spike protein—which is the target of our current vaccines—the T cells targeted internal proteins within the SARS-CoV-2 virus to prevent infection.
The researchers say these internal proteins offer a new vaccine target that could not only last longer—since T cells responses persist longer than antibody responses—but also help stem the tide of variant infection.
"The spike protein is under intense immune pressure from vaccine-induced antibodies, which drive evolution of vaccine escape mutants. In contrast, the internal proteins targeted by the protective T cells we identified mutate much less,” said Ajit Lalvani, senior author of the study and Director of the NIHR Respiratory Infections Health Protection Research Unit at Imperial. “Consequently, they are highly conserved between the various SARS-CoV-2 variants, including omicron. 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.”
While the study is small and limited in diversity to white European ethnicity, it is the first to provide direct evidence of a protective roll of T cells against SARS-CoV-2 infection.
Photo: Scanning electron micrograph of a T cell from the immune system of a healthy donor. Credit: NIAID