Antivirals need to be given as early as possible, before an infection takes hold, in order to be most effective. Merck tested its drug within five days of symptom onset.
“We saw that we did have high efficacy, even if it was five days after a patient has been treated … people might wait a couple of days before getting a test or something, and this means that we have time to treat people and really provide a benefit from a public health perspective,” Annaliesa Anderson, head of the Pfizer program, said.
The company did not detail side effects of the treatment, but said adverse events happened in about 20 per cent of both treatment and placebo patients.
“These data suggest that our oral antiviral candidate, if approved by regulatory authorities, has the potential to save patients’ lives, reduce the severity of COVID-19 infections, and eliminate up to nine out of 10 hospitalisation,” Pfizer Chief Executive Albert Bourla said.
Infectious disease experts stress that preventing COVID-19 through wide use of vaccines remains the best way to control the pandemic, but only 58 per cent of Americans are fully vaccinated and access in many parts of the world is limited.
Pfizer’s drug, part of a class known as protease inhibitors, is designed to block an enzyme the coronavirus needs in order to multiply.
Merck’s molnupiravir has a different mechanism of action designed to introduce errors into the genetic code of the virus. Merck has already sold millions of courses of the treatment, which was approved this week by UK regulators, to the US, the UK. and others.
Britain said earlier this month it had secured 250,000 courses of Pfizer’s antiviral.