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Common cold viruses may spark response against COVID-19 virus, La Jolla scientists report

The coronavirus known as SARS-CoV-2, shown in purple, infects a cell, colored in green.
The coronavirus known as SARS-CoV-2, shown in purple, infects a cell, colored in green.
(National Institute of Allergy and Infectious Diseases)

Some people who have never been exposed to the coronavirus may have protection against it, but that is far from certain.

Your chances of getting COVID-19 could depend partly on how your body reacted the last time you caught a cold, according to a new study by researchers at the La Jolla Institute for Immunology.

SARS-CoV-2, the virus that causes COVID-19, may be the latest coronavirus, but it’s not the first. There are four other coronaviruses, which can cause the common cold. The new study shows that some people who have never been infected with SARS-CoV-2 have immune responses to it because they’ve been exposed to what are essentially older cousins of the virus.

Scientists are still figuring out exactly what this means. But it’s possible that people with immune responses to the common coronaviruses may be less likely to get COVID-19, according to Alessandro Sette, one of the study’s senior authors.

“This may give you a head start,” Sette said. “If you have a head start, you may mount a faster response or a stronger response. You might not get as sick.”

Sette and colleagues published their findings Aug. 4 in the journal Science, but their discovery started with a puzzling observation months ago. That was when Sette’s team detected immune responses to the SARS-CoV-2 coronavirus in blood samples collected before the COVID-19 pandemic — meaning there was no way the samples came from people who had been exposed to the virus.

That finding has since been confirmed by studies of people from the United States, United Kingdom, Netherlands, Germany and Singapore. Those reports showed that between one-fifth and half of those who have never been exposed to the SARS-CoV-2 coronavirus may have an immune response to it.

But why? Sette’s team suspected that the four common coronaviruses were the answer. Perhaps some people’s immune systems had already seen pieces of the common coronaviruses that were nearly identical to the SARS-CoV-2 virus.

To put that theory to the test, researchers analyzed blood collected from San Diegans before the pandemic. They found all the areas of the coronavirus targeted by their immune systems and looked for regions of the four common coronaviruses that were nearly identical.

When the scientists used the matching viral regions to stimulate the cells of uninfected people, their immune cells revved up, suggesting that some of the cells could respond both to the previous coronaviruses and to the SARS-CoV-2 virus.

The findings, based on studying cells in a dish, don’t prove that exposure to previous coronaviruses protects against COVID-19. But if so, that would help explain why COVID-19 is deadly for some while others recover with hardly any symptoms (age and pre-existing conditions are clearly still important factors).

This sort of thing has happened before, according to Daniela Weiskopf, a researcher at the La Jolla Institute for Immunology who also was a senior author on the study. She cited the 2009 swine flu pandemic, during which adults 65 and older were less likely to get sick. Some researchers believe older adults benefited from a pre-existing immune response to a similar flu virus from decades earlier.

“It’s provocative and interesting,” said Dennis Burton, an immunologist at La Jolla’s Scripps Research Institute who was not involved in the study. “There’s still a step missing because you need to show this is important for immunity.”

Sette and Weiskopf believe data from ongoing COVID-19 vaccine trials could help address that missing piece by measuring T cells, immune cells that activate the parts of an antiviral response that kill infected cells and that produce antibodies, proteins that can grip the surface of a virus and prevent infection.

Both researchers say that studying T cell responses before and after a COVID-19 vaccine could help researchers interpret any person-to-person variation in how well a vaccine works.

It’s possible, Weiskopf said, that those who respond best to a vaccine will do so because they already have T cells to past coronaviruses that are ready to launch a swift counterattack. “That is something that we are very interested in and we are looking into.” ◆