As concern over the coronavirus grows, with over 100 possible cases in the U.S. and five confirmed, CBS News chief medical correspondent Dr. Jon LaPook told "CBS This Morning" that Americans should not panic. People who have never been to China or have not had contact with anyone who recently returned from there are "probably fine," he said.

Still, top health official Dr. Tony Fauci said "we have to prepare for the worst."

The CDC issued its strongest travel warning, urging Americans to cancel all non-essential trips to China. Global banking giants Credit Suisse and Goldman Sachs told staff on Tuesday morning they should stay home for at least 14 days if they have been to the country recently.

LaPook challenged what he said was a Chinese health minister's warning that a person could be contagious without showing symptoms, but said it would be "a big deal if it turns out you can infect somebody else and you don't have any symptoms."

Asked what people should be doing, LaPook's advice was to keep "monitoring the situation." The outbreak is hitting in the middle of flu season in the U.S., so LaPook urged people to get that vaccine so they do not confuse the symptoms.

Other precautions could be as simple as coughing into your arm, he added. However, one common defense might not be as effective as people think – face masks, he said, give only "partial protection."

"If it's a droplet, there's going to be virus in the droplets, so it will help protect it. But remember the virus is so small it can go through the mask," he said.

Germany and Japan recently announced coronavirus cases among patients who were not in Wuhan, but they did have contact with people from the city. LaPook dismissed any alarm over the update.

"That makes scientific sense," he said. "It would be one thing if there was no contact at all with somebody from Wuhan or the area. Remember that a lot of people, millions according to the mayor of Wuhan, left that city and that area before there was that so-called quarantine. So it makes sense, it's not magic."