The biggest test yet of an experimental COVID-19 vaccine got underway Monday with the first of some 30,000 Americans rolling up their sleeves to receive shots created by the U.S. government as part of the all-out global race to stop the pandemic. Final-stage testing of the vaccine, developed by the National Institutes of Health and Moderna Inc., began with volunteers at numerous sites around the U.S. given either a real dose or a dummy without being told which. Another company, Pfizer Inc., announced late Monday that it had started its own study of its vaccine candidate in the U.S. and elsewhere. That study also aimed to recruit 30,000 people. It will be months before results trickle in, and there is no guarantee the vaccines will ultimately work against the scourge that has killed over 650,000 people around the world, including almost 150,000 in the U.S. After volunteers get two doses a month apart, scientists will closely track which group experiences more infections as they go about their daily routines, especially in areas where the virus is spreading unchecked. Don’t expect a vaccine as strong as the measles vaccine, which prevents about 97% of measles infections, Fauci said, adding he would be happy with a COVID-19 vaccine that’s 60% effective.