What you need to know about coronavirus on Sunday, May 17

FILE - In this May 8, 2020, file photo, a team of medical workers wearing respirators and protective gear ready to enter the room of a patient in the COVID-19 Intensive Care Unit at Harborview Medical Center, in Seattle. The number of deaths in Washington because of the coronavirus has reached 1,000, the Washington State Department of Health reported Saturday, May 16, 2020. The agency added eight more deaths and listed the total number of confirmed cases at 18,288. (AP Photo/Elaine Thompson, File)
FILE - In this May 8, 2020, file photo, a team of medical workers wearing respirators and protective gear ready to enter the room of a patient in the COVID-19 Intensive Care Unit at Harborview Medical Center, in Seattle. The number of deaths in Washington because of the coronavirus has reached 1,000, the Washington State Department of Health reported Saturday, May 16, 2020. The agency added eight more deaths and listed the total number of confirmed cases at 18,288. (AP Photo/Elaine Thompson, File) (Copyright 2020 The Associated Press. All rights reserved)

(CNN) -- With the virus largely contained in China, life is slowly returning to normal there. Lockdowns have eased while some schools and factories have reopened.

But the country's top medical adviser, Dr. Zhong Nanshan, tells CNN that a potential second wave of Covid-19 infections remains a "big challenge." That's because we don't know whether people develop immunity to the virus after contracting it.

There have been worrying signs. Most recently, eight sailors from the aircraft carrier USS Theodore Roosevelt tested positive for the virus a second time.

Zhong also confirmed that local authorities in Wuhan, where the coronavirus was first reported in December, suppressed key details about the magnitude of the initial outbreak. "At the very beginning they kept silent, and then I said probably we have (a larger) number of people being infected," he said.

Fresh clusters of cases have emerged across China recently. On Friday more than 8,000 people were quarantined in and around Shulan, in the northeastern province of Jilin.

Fears of a potential second wave have also rattled South Korea, where confirmed cases believed to be linked to Seoul's nightclub cluster rose to 168 today.

Many from the country's LGBTQ community, which still faces discrimination in South Korea, frequent the nightclubs. And fears of having their sexuality outed have kept some patrons who were potentially exposed from coming forward.

As global leaders weigh the risk of second waves of infections with the need to reopen their economies, people are increasingly losing patience. Protests against lockdown measures spread this weekend in the United States, Germany and the United Kingdom.