Treating an active infection is another matter. There’s a pharmaceutical cure for only one virus: hepatitis C. Because of the “kill the virus, kill the host” problem, the best bet is often to slow the virus down enough that the body’s own defenses can do their job.

“When we can’t kill a virus, the best thing we can do is stop them from replicating,” said Raed Dweik, chair of the Cleveland Clinic’s Respiratory Institute in Ohio. “All we can do is shorten the period of infection, not cure. Even when the infection is over, the patient is more recovered than cured.”

Remdesivir, the only drug in wide use that targets SARS-CoV-2 itself, works by messing with the virus’s ability to replicate. It causes errors when the virus tries to copy itself. It was also a product of luck: the drug was originally developed as a treatment for Ebola, but it wasn’t terribly effective and the waning outbreak in Africa made it difficult for its manufacturer, Gilead Sciences Inc., to study. 

Clinical trials have shown that remdesivir can help hospitalized Covid-19 patients recover more quickly. But it’s not a cure, and it’s unlikely there will be one any time soon.

“It will take years to have potent and specific drugs that can stop coronavirus in its tracks,” Cannon said. “The vast majority of drug candidates fail.”

In the future, patients will likely get a cocktail of therapies that attack the virus and others that help keep them stable. Currently, remdesivir is part of a cocoon of care that includes the only other cleared therapy, the steroid dexamethasone, as well as standard fare like fluids, plus aggressive approaches when needed including putting patients on ventilators. Other medicines are layered on top: blood thinners and experimental approaches to calm a potentially overactive immune system.

As new approaches reach the market, they’ll be added to the mix. But for most people, any viral treatment will have to outperform an already formidable and existing approach: the human immune system.

The Best Defense
It’s not a coincidence that many  infections last for about two weeks, Cannon said. That’s how long it takes for the immune system to kick into gear.

“Our immune system is the world’s best drugmaker,” she said. “Whether you had measles as a 5-year-old or Covid as a 50-year-old, our immune system comprises this vast library of potential antiviral approaches that offer protection.”

Antibodies, the infection-fighting proteins produced to ward off foreign invaders, are biological drugs we make ourselves, Cannon said. The body has the ability to make millions and millions of them, activating just the right one when it binds to a virus – then mass producing it over a period of about 14 days.