Global disease experts say little is known about China's experience with long-term COVID effects thought to have afflicted millions with debilitating fatigue, brain fog and other symptoms
The oral antiviral drug will be studied in over 1,300 volunteers to see if it can prevent the spread of the coronavirus.
Merck said in June the US government has agreed to pay about $1.2 billion for 1.7 million courses of its experimental COVID-19 treatment, if it is proven to work in a separate, ongoing large trial and authorised by US regulators.
The new late-stage study is enrolling participants who are at least 18 years of age and stay in the same household as someone infected with symptomatic COVID-19.