While there are numerous effective and safe vaccines to prevent Covid-19, there are few drugs to treat those who have already contracted or been exposed to the virus. Those we do have – such as corticosteroids – tend to target the body’s response to infection, not the virus, and those that do actually target the virus – such as monoclonal antibodies like Regeneron – are expensive, in short supply and must be administered intravenously in hospital settings. An oral therapy could help eliminate many of the barriers to treatment and help keep people out of hospital.

Pfizer (PFE) said it is launching a mid-to-late-stage clinical trial to test whether the antiviral drug, PF-07321332, can prevent Covid-19 infection in some 2,660 healthy adults living in the same house as someone with a confirmed symptomatic infection.

The trial will test the safety and efficacy of the pill with ritonavir, another antiviral widely used to treat HIV. One third of patients in the trial will receive a placebo, while the remainder will receive a dose of the drug twice a day for either five or 10 days.