Sweeping testing of the entire crew of the coronavirus-stricken U.S. aircraft carrier Theodore Roosevelt may have revealed a clue about the pandemic: The majority of the positive cases so far are among sailors who are asymptomatic, officials say.

The possibility that the coronavirus spreads in a mostly stealthy mode among a population of largely young, healthy people showing no symptoms could have major implications for U.S. policy-makers, who are considering how and when to reopen the economy.

It also renews questions about the extent to which U.S. testing of just the people suspected of being infected is actually capturing the spread of the virus in the United States and around the world.

The Navy’s testing of the entire 4,800-member crew of the aircraft carrier - which is about 94% complete - was an extraordinary move in a headline-grabbing case that has already led to the firing of the carrier’s captain and the resignation of the Navy’s top civilian official.

Roughly 60 percent of the over 600 sailors who tested positive so far have not shown symptoms of COVID-19, the potentially lethal respiratory disease caused by the coronavirus, the Navy says. The service did not speculate about how many might later develop symptoms or remain asymptomatic.

“With regard to COVID-19, we’re learning that stealth in the form of asymptomatic transmission is this adversary’s secret power,” said Rear Admiral Bruce Gillingham, surgeon general of the Navy.

The figure is higher than the 25% to 50% range offered on April 5 by Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and a member of President Donald Trump’s coronavirus task force.