US pharmaceutical company Pfizer Inc (NYSE:PFE) has commenced a mid-to-late-stage study testing its investigational oral antiviral drug, PF-07321332, for the prevention of COVID-19 infection among those who have been exposed to the virus, Reuters news agency reported on Monday.

Pfizer said it would study the drug in up to 2,660 healthy adult participants aged 18 and older who live in the same household as an individual with a confirmed symptomatic COVID-19 infection.

The trial will reportedly test PF-07321332 with a low dose of ritonavir, an older medication widely used in combination treatments for HIV infection.

Pfizer had earlier said this month that it had started a mid-to-late-stage trial of PF-07321332 for the treatment of COVID-19 in non-hospitalised, symptomatic adult patients.