Bottom Line Up Front: When a coronavirus outbreak happens on your (non-passenger) ship don’t isolate and avoid it. Have a virus party instead!
Recent policy at MSC instructs mariners suspected of having COVID-19 to be isolated in their rooms with little to no contact with shipmates. They should not go to work, public areas, the gym or leave their room. Food is to be brought to the isolated mariner on disposable plates.
These measures are bound to fail. As we have seen with the Diamond Princess the virus will spread in a shipboard environment under semi-isolation.
Per WHO the COVID-19 virus has a transmission rate (R0) of about 2.2 which means each infected person will typically spread the virus to 2.2 others. The time from infection to infectious is about five to ten days (with shorter and longer times possible). That means the virus can expect to infect a population as follows given R0=2.2 and infectious period of 10 days:
Day 0: 1 infectious, 0 recovered, 1 total
Day 10: 2.2 infectious, 1 recovered, 3.2 total
Day 20: 4.8 infectious, 3.2 recovered, 8 total
Day 30: 10.6 infectious, 8 recovered, 18.6 total
Day 40: 23.4 infectious, 18.6 recovered, 42 total
Day 50: 51.5 infectious, 42 recovered, 93.5 total
Day 60: 113.4 infectious, 93.5 recovered, 206.9
Ships with an active case of COVID-19 can be expected to be under quarantine for about fourteen days after the last symptomatic person recovers. During that time no one can leave the ship for liberty or reliefs. The ship might be denied entry to a port.
Given that quarantine would be lifted after the last symptomatic person recovers and a typical commercial deep sea ship has between twenty to thirty crew the expected quarantine period would be 54 days. (40+14)
On more populated ships, like MSC, the quarantine would be even longer. An oiler (T-AO) should expect 64 days, dry cargo ships (T-AKE) should expect 74 days and the fast cargo ships (T-AOE) about 84 days of quarantine. Drill ships, oil rigs and such would face equally daunting quarantine periods.
Per WHO the fatality rate for the mariner demographic is promising. Below the age of 60 the fatality rate is almost the same as the seasonal flu. Preexisting conditions that increase fatality are also somewhat rare amount mariners. The typical mariner has a lower chance of death or complication from COVID-19.
Therefore given that shipboard transmission is all but unavoidable, that death or serous complication is unlikely and that long-term quarantine absolutely sucks, mariners who find themselves on a ship with an infected individual should try to become infected as soon as possible. If infected a mariner should try to infect as many shipmates as fast as possible.
Personal protective measures such as washing hands and touching your nose, eyes or mouth should be avoided. Coughing with an uncovered mouth should be practiced in the company of others. Ships should have virus parties. Isolation and containment should not be policy.
That way the infection can be done with and everyone can either get back to work (and overtime) or go home on leave or relief.