(Bloomberg) — Senior citizens with underlying health conditions should avoid activities such as a cruise, U.S. Vice President Mike Pence said after meeting with the cruise-line industry as the coronavirus outbreak raises concerns for ship operators.

“If you have a family member or are yourself, a senior citizen with a serious underlying health condition, this would be a good time to practice common sense and to avoid activities, including traveling on a cruise line, that might unnecessarily expose one to the coronavirus,” Pence said in Fort Lauderdale, Florida.

Health officials worldwide are struggling to contain an outbreak of the virus on cruise ships, which represent “ a unique challenge,” Pence said earlier this week. In the U.S., 21 people tested positive for the virus on a ship operated by Carnival Corp.’s Princess Cruises, which has been in limbo off the coast of California. More than 700 people on another Carnival vessel in Yokohama tested positive and were under quarantine for a time last month.

Adam Goldstein, global chair of the Cruise Lines International Association, told reporters the industry is committed to developing a plan so that “guests coming to us being with us and leaving us” are handled in a way appropriate for the public’s concerns.

Pence said the industry agreed to work on plans to quarantine passengers on land, rather than aboard ships that can turn into transmission vehicles for the virus.

“New quarantining standards will be coordinated with the CDC for all ships, and we also will be working with the industry as they develop a plan to move any patients that contract the coronavirus or otherwise become seriously ill to land-based facilities,” Pence said.

The Centers for Disease Control and Prevention, the Department of Homeland Security and the U.S. Coast Guard have been directed to work with the cruise industry over the next 72 hours on a plan, Pence said.

“We have committed to do even more to protect our guests, our crew and the communities where we sail,” the cruise association said in an email after meeting. “We expect to report back this week with further details.”

Carnival, Royal Caribbean Cruises Ltd. and Norwegian Cruise Line Holdings Ltd. have seen their market values crushed by at least 43% since the beginning of this year as the virus continues to spread throughout the world.

In response, operators are offering steep discounts for trips and have been refusing to allow guests who traveled from countries such as China, Iran and Italy, which have been hit the hardest so far by the virus.