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On Monday, the global health arm of the United Nations reported seven possible vaccines had been given the green light for testing.
One of the groups approved for clinical trials on humans is from the United States. Four are from China, one is from England and the last is made up of both Americans and Europeans.
The American National Institutes of Health (NIH) trial was the first to start testing on human subjects on March 16.
The NIH received $1.8 billion last week in the most recent stimulus package approved by Congress, bringing the agency's funding to $3.6 billion to combat coronavirus.
According to a tally from Johns Hopkins University, there have been 3.2 million cases of coronavirus confirmed globally and more than 231,000 deaths. In the United States, there have been more than 1 million cases of coronavirus and more than 61,000 deaths.
COVID-19 was first detected in Wuhan, the capital city of central China's Hubei province, in late 2019.