Summer may decide fate of leading shots in vaccine race

People on six continents already are getting jabs as the race for a COVID-19 vaccine enters a defining summer. The U.S. is poised to start even bigger studies next month to prove if any shot really works, a challenge as researchers chase a virus that’s waxing and waning around the globe. Already British- and Chinese-made vaccines are being tested abroad. And experts want to set public expectations: Even if first doses of a vaccine arrive by year’s end, don’t expect perfect protection — and do expect a long line as countries prioritize who gets vaccinated first.