Faced with legal cases against it alleging discrimination against the cruise industry, The US Centers for Disease Control and Prevention on Wednesday June 16th lowered its health notice on cruise travel from Level 4 (very high), which recommends avoiding all travel, to Level 3 (high).
The CDC is still recommending that people who are not fully vaccinated avoid any travel on cruise ships, including river cruises, worldwide, because the risk of Covid-19 on cruise ships is high. It is especially important that people who are not fully vaccinated who are more likely to get severely ill avoid travel on cruise ships, including river cruises. Cruise passengers who are not fully vaccinated against Covid-19 are at increased risk, since the virus spreads person-to-person, and outbreaks of Covid-19 have been reported on cruise ships because of their congregate (group) settings where Covid-19 spreads easily, the CDC said.
https://wwwnc.cdc.gov/travel/notices/covid-3/coronavirus-cruise-ship