MUMBAI: In a significant scientific milestone, an antiviral pill has, for the first time, been shown to prevent COVID-19 infection in people exposed to the SARS-CoV-2 virus within their own homes, according to trial results published in the New England Journal of Medicine.

The drug, ensitrelvir, developed by Japanese pharmaceutical company Shionogi, offers new hope particularly for vulnerable populations who continue to face serious risks from the virus even years after the peak of the pandemic.

Conducted internationally between June 2023 and September 2024, the Phase 3 trial involved more than 2,000 individuals who had been exposed to a household member showing COVID-19 symptoms. Participants were given either a five-day course of ensitrelvir or a placebo within 72 hours of exposure.

The results were compelling. In the placebo group, 9% developed symptomatic COVID-19, compared to only 3% in the ensitrelvir group — a remarkable two-thirds reduction. When including both symptomatic and asymptomatic infections, the confirmed infection rate dropped from 21.5% in the placebo group to 14% among those who received the drug. The pill also demonstrated a clear reduction in viral transmission within households.

Ensitrelvir works by blocking a key enzyme that coronaviruses need to replicate inside human cells. While it targets the same viral protein as Pfizer’s Paxlovid, ensitrelvir has succeeded where nirmatrelvir (Paxlovid’s main component) previously failed in preventing household infections.

Study co-author Frederick Hayden, a clinical virologist at the University of Virginia School of Medicine, highlighted the drug’s potential value for high-risk individuals. “As a 78-year-old with comorbidities, I certainly would use it if I had a known exposure,” he said.

The breakthrough is expected to be especially beneficial for care-home residents, organ transplant recipients on immunosuppressant drugs, elderly people with multiple health conditions, and other immunocompromised individuals. For the general population, the real-world impact may be more limited given the milder nature of circulating variants today.

Experts believe ensitrelvir could serve as an important safety net during future surges or local outbreaks. Health authorities worldwide are now reviewing the data for potential regulatory approvals.

This development marks an important addition to the COVID-19 toolkit, complementing vaccines and existing treatments. While it may not return society to emergency mode, ensitrelvir represents meaningful progress in managing the virus as an ongoing health concern rather than a global crisis.