Hence triggering these defenses by treating patients with interferons (an immune system protein that is also available as a drug) early in the course of COVID-19 infection may help in preventing or treating the infection.
‘Exposure to the rhinovirus, the most frequent cause of the common cold, can protect against infection by the SARS-CoV-2 virus which causes COVID-19 by jump-starting the activity of interferon-stimulated genes. This highlights the importance of interferon treatment as a possible benefit early in infection, but not when given later.’
On the contrary, previous studies suggest that high interferon levels at the later stages of COVID-19 correlated with worse disease outcomes via overactive immune responses.
Interferon-therapy for COVID-19
The team thereby studied this defense system early in the course of COVID-19 infection by infecting a lab-grown human airway tissue with SARS-CoV-2.
It and found that for the first three days, viral load in the tissue doubled about every six hours. However, the replication of the COVID-19 virus was completely stopped in tissue that had been exposed to rhinovirus. On blocking these antiviral defenses, the SARS-CoV-2 could replicate in airway tissue previously exposed to rhinovirus.
However, in the low dose of the infection, the same defenses slowed down SARS-CoV-2 infection even without rhinovirus. This suggests that the viral load at the time of exposure makes a difference in whether the body can effectively fight the infection. The team also confirmed their findings from the nasal swab samples of patients diagnosed at the start of infection.
“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. There are hidden interactions between viruses that we don’t quite understand, and these findings are a piece of the puzzle we are just now looking at,” says Ellen Foxman, assistant professor of laboratory medicine and immunobiology at the Yale School of Medicine and senior author of the study.
The study thereby derives the importance of interferon treatment as a possible benefit early in infection, but not when given later. Thus interferon treatment could be used prophylactically given in people at high risk who have been in close contact with others diagnosed with COVID-19.