RHODES, Greece—Greece began opening to tourists on April 19 with few bookings but hopes for a better season to help make up for the devastation of the pandemic measures in 2020. On the island of Rhodes, where most visitors come from abroad, hoteliers are scrubbing, polishing, and painting in anticipation of a make-or-break year. “We’re preparing the hotel in order to start as soon as the government gives us the green light,” said George Tselios, general manager of Sun Beach Hotel, whose customers are from Scandinavia, Germany, Austria, and the UK. Greece will formally open on May 14, but starting on April 19, tourists from the European Union, the United States, Britain, Serbia, Israel, and the United Arab Emirates will no longer be required to quarantine if they are vaccinated or test negative for COVID-19. Tourism, which generates a fifth of Greece’s GDP and 1 in 5 jobs, is vital …