Royal Caribbean Cruises Ltd.’s ship Explorer of the Seas is returning two days early to its New Jersey port after a stomach illness struck more than 600 people out of about 4,200 onboard, NBC News reported late Sunday. The 564 passengers and 47 crew members on the 10-day cruise to the U.S. Virgin Islands reported symptoms suggesting a possible norovirus outbreak, the report said, citing an official with the Centers for Disease Control and Prevention. The incident follows the outbreak of a gastrointestinal illness aboard another ship earlier this month.