Pfizer Shares Tumble After Study Finds Firm's Antiviral Drug Unable to Prevent COVID Infection

Paxlovid is a protease inhibitor oral antiviral drug that has been shown to be effective in treating COVID-19 patients with severe symptoms. There was hope that it could be used as a preventative medicine.

Pfizer’s share price recently dropped 2.6% after the company released a study showing its antiviral drug Paxlovid is not effective in preventing sickness in those exposed to the novel coronavirus.

The study looked at 2,957 patients who tested negative and were displaying no symptoms but were in the household of a symptomatic COVID-19 patient in the previous four days. Half of the study’s participants were given a placebo, whereas the other half received either a 5-day or 10-day supply of Paxlovid. Patients who took Paxlovid saw a slight decrease in symptomatic infection, 32% to 37%, but not enough to be statistically significant.

Paxlovid is still considered effective in treating symptomatic patients that have tested positive but the idea of using it as a prophylactic drug took a big hit with the release of the study’s results.

Despite this setback, Paxlovid is still set to be one of the fastest selling drugs of all time. Pfizer said it expects to sell $24 billion worth of the antiviral drug in 2022.

Preventative care was never expected to be a large part of Paxlovid sales, at least not initially. However, if it did show promise, there was potential it could have been used as a preventative drug before being in high risk situations, such as traveling or working in a hospital.

Pfizer’s stock dropped from $49.08 per share to $47.79 from the market’s open to 9:45am EST, a drop of 2.62%. It has since rebounded to $48.35 as of 4PM EST Monday, a 1.48% drop since the market opened at the start of the week.

There is still hope that other protease inhibitor oral antivirals may have some efficacy as a prophylactic treatment for COVID-19. There are other drugs in development, including those from Enanta Pharmaceuticals and Pardes Biosciences. It’s anticipated that officials may use the study on Paxlovid to learn in what scenarios their experimental protease inhibitor antivirals may be most effective.

This is the second bit of bad news to come out for Paxlovid in the past few weeks. Last week, reports started emerging about patients relapsing after their treatment ended, albeit with reduced symptoms.

“While we are disappointed in the outcome of this particular study, these results do not impact the strong efficacy and safety data we’ve observed in our earlier trial for the treatment of COVID-19 patients at high risk of developing severe illness,” said Pfizer CEO Albert Bourla in a statement. “We are pleased to see the growing global use of Paxlovid in that population.”