Washington, Dec 30 : The US Centers for Disease Control and Prevention (CDC) is investigating more cruise ships due to new Covid-19 cases aboard. A total of 88 vessels are under CDC's investigation or observation for Covid-19 outbreaks. Four other vessels are also being monitored by the US health agency, according to the latest data on the agency's website. CDC will follow up with cruise ships when an investigation is required as ships begin to sail with passengers on simulated or restricted voyages under the agency's Temporary Extension & Modification of Framework for Conditional Sailing Order, said the agency. While cruising will always pose some risk of Covid-19 transmission, CDC is committed to working with cruise ship operators to ensure that cruise ship passenger operations are conducted in a way that reduces the risk of Covid-19 transmission among crew members, passengers and port personnel, the agency added on its website. Covid-19 cases are surging to record high again as the Omicron variant continues to drive extremely high infection levels, Xinhua news agency reported. The country registered a grim new record of over 510,000 daily Covid-19 cases on Monday, according to data of Johns Hopkins University. /IANS