Portugal’s health care system was on the verge of collapse. Hospitals in the capital, Lisbon, were overflowing and authorities were asking people to treat themselves at home. In the last week of January, nearly 2,000 people died as the virus spread. The country’s vaccine program was in a shambles, so the government turned to Vice Adm. Henrique Gouveia e Melo, a former submarine squadron commander, to right the ship. Eight months later, Portugal is among the world’s leaders in vaccinations, with roughly 86% of its population of 10.3 million fully vaccinated. About 98% of all of those eligible for vaccines...