Dr. Mike Ryan, executive director of the World Health Organization health emergencies program, said the lives of people across the world could face “significant alteration” until a coronavirus vaccine is developed.

“There is a path out, but we must remain ever vigilant. And we may have to have a significant alteration to our lifestyles, until we get to a point where we have an effective vaccine, or an effective treatments,” Ryan said at a briefing Friday.

To reopen, “many countries are taking a very careful step-wise approach, relying on the patience and perseverance of their citizens to continue to suffer what is a difficult process both socially psychologically and economically for many people,” he said. “I think everyone is doing that because we want to protect those we love.”

Ryan sees the path out involving partial school openings, partial returns to workplaces and careful measures in high-density areas.

But for events like concerts and sports, he said, “it’s going to be much more difficult to make those perfectly safe.”