A new study published in the Journal of Experimental Medicine found that exposure to the virus that causes the common cold can give protection against infection by the SARS-COV-2.
The research states that rhinovirus, the common respiratory virus, kick starts the activity of interferon-stimulated genes and it triggers early-response molecules in the immune system which can stop reproduction of the SARS-COV-2, the virus that causes COVID-19, within the airway tissues infected with the cold.
Activating these defenses early in the course of COVID-19 infection has the capability to prevent or treat the infection. One way to do this is by treating patients with interferons, an immune system protein that is also available as a drug. But it all depends upon the timing, said senior study author, Ellen Foxman, assistant professor at the Yale School of Medicine in the US.
Earlier studies showed that at the later stages of COVID-19, high interferon levels are associated with worse disease outcomes, and may fuel overactive immune responses.
However, recent genetic studies found that interferon-stimulated genes can also be protective in cases of COVID-19 infection. The researchers wanted to study this defense system early in the course of the infection.
To study whether rhinoviruses would have a beneficial impact against the SARS-CoV-2 virus. The team infected lab-grown human airway tissue with the virus and found that for the first three days, viral load in the tissue doubled about every six hours. However, the researchers found that reproduction of the COVID-19 virus was completely stopped in tissue that had been exposed to rhinovirus.
If antiviral defenses were blocked, the SARS-COV-2 could reproduce in airway tissue previously exposed to rhinovirus. The same defenses slowed down SARS-COV-2 infection even without rhinovirus, but only if the infectious dose was low.
The result suggests that the viral load at the time of exposure makes a difference in whether the body can effectively fight the infection, the researchers noted.
The researchers also examined nasal swab samples from patients diagnosed close to the start of the infection and found evidence of rapid growth of SARS-COV-2 in the first few days, followed by activation of the body’s defenses.
According to their findings, the virus typically increased rapidly for the first few days of infection, before host defenses started, doubling about every six hours as seen in the lab. In some patients the virus grew even faster, the researchers found.
“There appears to be a viral sweet spot at the beginning of COVID-19, during which the virus replicates exponentially before it triggers a strong defense response,” Ms. Foxman said.
The interferon treatment holds promise but it could be tricky because it would be most effective in the days immediately after infection when many people exhibit no symptoms. Trials of interferon in COVID-19 are underway, and so far show a possible benefit early in infection, but not when given later.