FILE - In this Wednesday, June 24, 2020 file photo, a volunteer receives a COVID-19 test vaccine injection developed at the University of Oxford in Britain, at the Chris Hani Baragwanath hospital in Soweto, Johannesburg, South Africa. People on six continents are testing experimental shots as the race for a COVID-19 vaccine enters a defining summer, with even bigger studies poised to prove if any leading candidate really works - and possibly offer the public a reality check. (AP Photo/Siphiwe Sibeko)
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