Last year, Thailand was one of the world's top performers at fighting the coronavirus. It sacrificed the tourism dollars that normally buoy its economy to shut out Covid-19. In September, it celebrated 100 consecutive days of no locally transmitted infections.

The government is now making a stark departure from that vision of an infection-free oasis. Its new message: Learn to live with the virus long term.

Thailand has been struggling to contain a monthslong surge in infections, fix a faltering vaccine rollout and combat growing impatience among citizens over its battered economy. Its recalibration shows how several developing countries—even those that fared well for months—are battling crises on multiple fronts as richer nations inoculate rapidly and reinvigorate their economies.

Prime Minister Prayuth Chan-ocha pledged this week to fully reopen the nation in the next 120 days, or by mid-October, allowing most restrictions on business and tourism to be lifted. Foreign visitors would have to be vaccinated but could enter and travel freely. Doing so, he said, would mean accepting higher infection rates, but the step is necessary to ease the enormous suffering of those struggling to earn a living.