The short answer is: Yes and no. The long answer is: It depends.
What does quarantine mean? A quarantine is an isolation of infected people from the non-infected population. This may be imposed by force through a government, as done in China at the moment. It may also be a voluntary separation from others. In both cases, the aim is to stop the spread of an infectious disease.
When is it wise to impose a quarantine? It makes sense if the infectious disease is spread by droplets or close body contact (i.e. with hemorrhagic patients). It makes sense if the disease is spread only after symptoms have started. In such cases infected patients can be separated before they spread the disease. This was successful in the recent Ebola outbreaks on the African continent. Ebola is a fast- acting virus, patients become severely ill before they spread the virus. If a pathogen is transmitted before the onset of symptoms, a quarantine will have little or no effect.
In short, in order to efficiently contain the disease, the quarantine must be in place before patients spread the pathogen. Unfortunately, this was not the case with COVID-19. While the drastic measures by the Chinese authorities may slow down the spread, they will not contain the disease.
However, the slowing down of a spread together with early information does give other regions and countries a chance to prepare for such an epidemic. People traveling from epidemic areas, who might have contracted the pathogen, may be kept under surveillance. Such measures have been put into place in several countries.
One critical issue is the impact on societies. Once quarantines are discussed, it is easy to cause panic. People will want to get out of the area as fast as possible, with some of them carrying the disease. Another aspect is the understandable tendency of people to try and hide the infection. This is especially the case when stigmatization takes place. So, mass quarantine is a drastic measure that needs careful decision-making. Otherwise it may produce more harm than good.
Which brings us to the quarantine of a cruise ship. This reminds us of the classic quarantine: It was a measure often put into place during the Plague epidemics in Europe. Venice was an economic super-power of its time. Trade with many countries was the foundation of their success and wealth. Ships from around the known world arrived. Knowing that the disease took weeks to develop, the Venetian harbor was closed for ships from Plague-ridden areas. The ships had to wait at sea for forty days (hence the term ‚quarantine‘), before they were allowed to disembark. In many cases, when Plague was on board, all the seamen were infected in the end. (At this time, it was not known that Plague was transmitted by a flea, carried by rats, that were still present on board.) Now, Plague was as deadly as an infectious disease may be, 30 % of the European population were killed by the disease. Compared to such numbers, the current coronavirus outbreak is not such a menace.
Keeping thousands of people on board of a cruise ship was a recipe for disaster. Shared facilities, air conditioning and ventilation systems, lack of hygienic measures, led to hundreds of people being infected. Luckily, COVID-19 in most cases is a mild disease.
Take care,
Sabine and Joerg