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The 195 Americans evacuated from the Chinese city at the center of the new virus outbreak are undergoing three days of testing and monitoring at a California military base to ensure they do not show signs of the illness, officials said Wednesday.

The people flown out of China on a plane chartered by the U.S. government have not been quarantined, Dr. Chris Braden of the Centers for Disease Control and Prevention told reporters after the plane landed at March Air Reserve Base.

Authorities said those evacuated, including U.S. consular employees based in the Chinese city of Wuhan and families with children, are technically not required to stay on the base. But all 195 passengers have agreed to stay for up to three days while they are evaluated for the illness that’s infected thousands and killed more than 100, the CDC’s Dr. Nancy Messonnier said.

Officials initially said there were 201 passengers, but the CDC said later that number included the six members of the plane’s crew.

If any passengers decide they want to leave the base 60 miles (96 kilometers) east of Los Angeles before full medical evaluations are completed, U.S. officials would discuss their request, said Dr. Nancy Knight of the CDC.

“They are sitting in the middle of a military base,” Knight said. “Any discussion around departure would be just that: it would be a discussion.”

Braden described people as being “very happy to be here,” where they’re getting housing, medical attention and testing for the virus.

“They wanted to know their status,” he said.

Officials could quarantine any of those evacuated on a case-by-case basis if officials determine they need to do so, Braden said.

It can take up to 14 days for someone who is infected to develop symptoms, health officials believe.

If passengers from the chartered flight show no signs of the virus and leave the base, they will continue to be monitored by public health officials at their destinations for the remainder of a period lasting 14 days, he said.

Symptoms of the virus include fever, cough and in more severe cases, shortness of breath or pneumonia.

None of the passengers showed signs of having the virus when they were screened before leaving Wuhan, the epicenter of the virus, or when they were screened again during a refueling stop in Anchorage, Alaska.

The jet landed at the California base shortly after 8 a.m. A ground crew dressed in white approached the aircraft, and three charter-style buses parked near the plane. About 40 minutes after landing, people could be seen walking from the plane to the first bus, which then departed. Another bus pulled up next to the plane’s baggage compartment.

All the passengers already underwent two health screenings in China and the CDC screened them twice more in Anchorage. One passenger received medical attention for a minor injury that happened before boarding the airplane in China, Dr. Anne Zink, Alaska’s chief medical officer, told reporters after the plane left.

Some of those expected on the flight from Wuhan were not allowed to board because they did not have documents they needed to enter the U.S., Braden said. One person with a fever also was denied boarding, he said.

Wuhan is the epicenter of a new virus, which has largely sickened people in China and where all the deaths have been. China has cut off access to Wuhan and 16 other cities in Hubei province to prevent people from spreading the virus farther.

In addition to the United States, countries including France, Britain, Canada, Australia and New Zealand have planned evacuations of their citizens from Wuhan.