I would just assume everyone on board is sick, and let the people roam freely.
At first maybe only 10 persons are infected.
Everyone is allowed to roam.
Infection rate roars, soon everyone is infected.
Responders are now at a higher risk of being infected.
Trash piles up, thrown overboard or must be collected by people coming and going, all increasing the risk of infection beyond.
Food and other supplies must be brought in, increasing chances of contact and infection with those who deliver the supplies, so supplies are delivered by drone.
Responders stay on board permanently to reduce risk of transmission beyond.
Sanity goes down.
Cruise ship is abandoned as cases soar throughout the world beyond as treatment or containment capacity and resources are no longer available.