"We knew that people with severe forms of the disease developed antibodies within 15 days of the onset of symptoms", said Arnaud Fontanet, head of the global health department at the Institut Pasteur, which conducted the research with the University Hospital in Strasbourg.
A new study of COVID-19 patients in China revealed that 42% of patients who presented no symptoms were contagious for less time than those showing symptoms.
Note that passengers who had traveled through countries with high rates of infection were not allowed passage. One of the most important findings of the study, the researchers said was that the majority of COVID-19-positive patients, about 80 per cent, did not exhibit any symptoms.
They explain that despite taking certain precautions, such as taking everyone's temperature before embarking and making hand-sanitising stations readily available on board, especially in the dining room, the first case of fever was reported on day eight of the expedition. More than half (59 per cent) tested positive.
The ship arrived in Uruguay on day 13, where eight passengers and crew eventually required medical evacuation to hospital for COVID-19-related respiratory failure.
However, whether or not those who have been infected are immune is yet to be determined, the scientists said, adding that there is a pressing need for accurate global data on the total number of infected people.
In 10 instances, two passengers sharing the same cabin didn't have the same test result, possibly because the current swab test returns a substantial number of false-negative results, the authors said.
The Uruguayan government and Ministry of Health provided a "sanitary corridor" for the repatriation of 112 Australian and New Zealand passengers on day 28 and for all other passengers on day 32.
The study authors concluded the incidence of the virus on cruise ships was anticipated to be "significantly underestimated", plus they warned passengers must be tracked after boats set sail to ward off neighborhood disperse of the virus.
He said: "It is hard to find a reliable estimate of the number of Covid positive patients who have no symptoms".
Professor Alan Smyth, the joint editor of the journal Thorax, said: "A high proportion of infected, but asymptomatic, individuals may mean that a much higher percentage of the population than expected may have been infected with COVID".
He also notes that, "It is hard to find a reliable estimate of the number of Covid-positive patients who have no symptoms", adding that the 1 per cent suggested by the World Health Organization in early March is much lower than the number found on the cruise ship.
Based on the potentially high rate of false negative results obtained with the current swab tests, they suggested that secondary testing is warranted.