Royal Caribbean International, Celebrity Cruises and Silversea Cruises will require their crew members to receive the COVID-19 vaccine before they can resume working onboard. This was revealed by Crew Center in a letter sent to crew, and also later obtained by Cruise Industry News.

“So far, several vaccines have shown to be effective at preventing both mild and severe symptoms of COVID-19, and we intend to make them a key component of our healthy return to service. Therefore, we expect vaccinations will be required for our crew as part of our plan for your return to working on our ships,” the company wrote in a letter to its crew members.

Royal Caribbean Group said that they are “working on the details” and “cannot yet answer questions about how, when or where” the crew can get their vaccines.

“The process may be different depending on where you live, the timing of your next contract and whether you are already onboard or traveling. We appreciate your patience as we work through these details,” the company wrote.

It added that it will be able to update the crew on “what to expect” in the coming weeks.