Treatment Within 72 Hours of COVID-19 Exposure: Xocova Launches in the US, Filling the Oral Prophylaxis Gap

COVID-19 vaccines are designed for use before exposure to the virus, while treatments generally intervene after infection has been established. Now, for the first time in the United States, an oral prescription drug has been approved to fill the gap between the two. Shionogi announced that Xocova (ensitrelvir) has launched in the US for post-exposure prophylaxis in adults and adolescents aged 12 years and older following contact with a person with COVID-19.

The US Food and Drug Administration (FDA) approved this indication on May 29. Under the approved labeling, treatment must begin as soon as possible after exposure and no later than 72 hours afterward. The dose is 375 mg on the first day, followed by 125 mg once daily from the second through fifth days. Xocova inhibits the main protease required for viral replication, with the aim of suppressing viral proliferation before the infection develops into symptomatic disease.

The approval was based primarily on the global Phase 3 SCORPIO-PEP trial. The study enrolled 2,387 household contacts who had no symptoms and tested negative on a rapid test at screening; the primary analysis included 2,041 participants confirmed by a central laboratory to be negative at baseline. Within 72 hours after symptoms appeared in an infected household member, participants were randomly assigned to receive five days of Xocova or placebo.

By Day 10, 2.9% of participants in the Xocova group had developed symptomatic COVID-19 infection, compared with 9.0% in the placebo group, corresponding to a 67% relative risk reduction and an absolute difference of 6.1 percentage points. Overall adverse-event rates were similar between the two groups, at 15.1% and 15.5%, respectively; serious adverse events occurred in 0.2% of each group. No COVID-19-related hospitalizations or deaths occurred in the trial, but the absence of such events also means the study could not determine whether the drug reduces the risk of severe disease or death.

The boundaries for applying these data are clear: the study population consisted of close household contacts, the primary efficacy endpoint focused on the ten days after exposure, and more than 98% of participants had evidence of antibodies resulting from previous infection, vaccination, or both. The results therefore cannot be directly extrapolated to every exposure setting, nor can the drug replace the longer-term protection provided by vaccination.

Safety considerations will likewise shape real-world use. Xocova has important CYP3A drug interactions and must not be used with certain antiepileptic, lipid-lowering, and other medications. The labeling also warns of embryo-fetal toxicity and serious hypersensitivity reactions. Children under 12 years of age are not currently included in the US approval, and the FDA has required Shionogi to complete deferred pediatric studies within specified deadlines.

Background

Xocova is approved in the US for post-exposure prophylaxis, not for treating confirmed COVID-19 infection. It adds an option that must be initiated rapidly for household members or other clearly identified close contacts, but it also makes determining the time of exposure, obtaining a prescription promptly, and reviewing existing medications critical to whether its efficacy can be realized. As the COVID-19 response gradually returns to routine medical care, the drug’s value will ultimately depend not only on its efficacy in trials, but also on whether clinical processes can operate smoothly within the 72-hour window.