Harnessing those capabilities in a drug, though, is not easy. Interferons can trigger wide-ranging side effects, including inflammation, a risk in Covid cases because some patients have an overactive immune response.
“You basically tell your body you’re being highly infected by a virus, and to fight, fight, fight at all costs,” said Juliet Morrison, a microbiologist at the University of California, Riverside.
Previous studies had tested interferon treatments only on patients who were already sick and in the hospital. That meant that the drugs were often administered too late, leading to mixed or disappointing results.
The scientists behind the Eiger drug envisioned a clever workaround.
With hepatitis treatments in mind, they had previously acquired a drug based on lambda interferons, a lesser-known type of interferon whose receptors are largely restricted to specific areas, like the respiratory tract. That happened to be precisely where the coronavirus was replicating. And it meant that the side effects would theoretically be less intense than those from the more commonly used class of interferons, whose receptors are throughout the body.
Those hopes were borne out in the latest trial. After administering the shot to about 900 patients and giving another 1,000 patients a placebo, the researchers found no appreciable difference in the incidence of side effects, they said.
Vaccination kept the vast majority of patients in both groups safe from hospitalization or a prolonged emergency department visit. But treating patients with interferon within a week after they noticed symptoms halved their chances of being hospitalized: Twenty-five people given the shot were hospitalized, compared with 57 who had not been treated.
The effects were even more pronounced when the drug was given within three days of symptoms developing, and when it was given to unvaccinated people. Most of the patients in the study were at relatively high risk from Covid — either because they were 50 or older, or because they had an underlying condition or a weakened immune system.