The new regimens, which require 30 or 40 pills to be taken over five days, have been shown to dramatically reduce hospitalizations and prevent deaths in adults with mild to moderate Covid who are at risk for severe disease because of age or underlying conditions.

But experts say the success of the treatments would hinge on one uncertain factor: whether high-risk patients infected with Covid will be able to get tested — and then treated — fast enough to make a difference.

Erica Johnson, who chairs the Infectious Disease Board of the American Board of Internal Medicine.

and Ridgeback Biotherapeutics, was given to non-hospitalized, unvaccinated, high-risk adult patients within five days of their first covid symptoms.

Pfizer’s product, Paxlovid, was tested in similar patients as early as three days — just 72 hours — after symptoms emerged.

But those promising results assume the drugs can be administered in the narrow window of time used in the trials, a proven challenge when getting antiviral treatments to actual patients.

Similar drugs can prevent dire outcomes from influenza if given early, but research shows that only about 40 percent of high-risk patients during five recent flu seasons sought medical care within three days of falling ill.

“That’s just not human nature,” said Kelly Wroblewski, director of infectious disease programs for the Association of Public Health Laboratories.

Even when patients do seek early care, access to Covid testing has been wildly variable since the start of the pandemic.

Department of Health and Human Services officials have said that the antiviral treatments will be distributed through the same state-based system adopted for monoclonal antibody treatments.

The lab-made molecules, delivered via IV infusion or injection, mimic human antibodies that fight the Covid virus and reduce the risk of severe disease and death.

Still, the antiviral pills won’t replace the antibody treatments, said Dr

“We’ll be on an interesting tightrope in which we’ll be trying to identify eligible patients early on to treat them with antivirals,” Webb said