Scientists Say the Common Cold Can Keep the Flu at Bay. Can It Do the Same for Covid-19?

(CN) — The rhinovirus that causes the common cold may pose an effective deterrent to influenza, according to new research from Yale University — and could potentially help quell the onslaught of Covid-19 cases.

Scientists studied clinical data from the 2009 H1N1 pandemic in Europe to determine if physiological changes induced by the common cold can help stave off the flu. They found the rhinovirus, the most common cause of a cold, jump-starts a piece of the body’s immune system and often prevents an infected person from simultaneously coming down with the flu.

Researchers looked at three seasons worth of data from more than 13,000 patients seen at Yale New Haven Hospital to determine how rhinovirus infection affects subsequent H1N1 flu infection in a new study published Friday in the journal Lancet Microbe.

“During the 2009 swine flu pandemic, throughout Europe scientists noticed that the expected wave of flu transmission seemed to be delayed by the common cold season which occurs every autumn after school begins,” said Ellen Foxman, assistant professor of laboratory medicine and immunobiology at Yale University and senior author of the study, in an email interview. “This led to a lot of speculation that rhinovirus, the common cold virus, may have prevented the spread of the pandemic flu virus.”

To test that hypothesis, Foxman’s team grew human airway tissue, called epithelial cells, in a lab from differentiated stem cells. These are the cells lining the lung and are most commonly infected when a person comes down with a respiratory illness. They inoculated the cells with rhinovirus, waited three days, then inoculated the same cultures with H1N1.

They noted a substantial reduction in H1N1 viral RNA five days after exposure to the rhinovirus. It turns out the rhinovirus had prompted the immune system to ramp up production of interferon, a natural immune response that prevented the flu virus from taking hold.

“We were surprised by how effective the common cold virus was at preventing flu infection — in cells exposed to the common cold virus three days prior, there was a ~50,000 fold drop in the amount of flu produced compared to cells which had not seen the common cold virus,” Foxman said.

To verify their findings, the researchers blocked the cells’ interferon response and found the H1N1 virus continued to replicate normally in its absence. This may help explain why few H1N1 cases occurred in the winter of 2009, a time when the common cold was raging across Europe.

The results are tantalizing because they show viral interference can have a major effect on the course of a pandemic — and could potentially be applied to a treatment for Covid-19. Though Foxman noted it’s still too early to tell for sure.

“It is impossible to predict how two viruses will interact without doing the research,” Foxman said in a statement.

To evaluate their results the researchers counted instances of single and concurrent infections for a number of different virus combinations. They then “estimated the expected number of co-infections in the absence of interference for all virus pairs.” Next, they applied statistical analysis to determine whether a significant difference exists between the two figures, evidencing a pattern, or if the findings were just a fluke.

They found “seasonality consistent with other studies, with wide peaks of rhinovirus positive samples each autumn and spring, and a narrower peak of IAV positive samples between the rhinovirus peaks each winter,” according to the study. The results show that the number of individuals infected with both viruses during months of peak co-circulation was significantly lower than expected, and outside the realm of chance.

Researchers noticed that rhinovirus replicated swiftly in human epithelial cultures during the first 24 to 48 hours and plateaued around day three. At this point the cultures displayed significant signs that an interferon response had been deployed to combat the virus, which subsequently prevented the H1N1 virus from replicating.

Foxman’s lab has already begun looking into whether the rhinovirus can prompt similar results in patients infected with the SARS-CoV-2 virus that causes Covid-19.

“Current studies suggest that exposure to interferon early in SARS-CoV-2 infection, when the virus is still replicating the airway, can be effective in helping the body clear the infection faster,” she said.

“Triggering interferon responses is how the common cold virus prevented flu infection in our study.  However, each virus is different and we cannot predict the exactly how SARS-CoV-2 will interact with other respiratory viruses just yet; this requires further study.”

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