Diamond Princess Offered Scientists with Opportunity to Research on Coronavirus

Diamond Princess, had been brought into the spotlight when the entire cruise ship with more than 3,000 passengers on board, was quarantined in Japan for a long period. The incident leading to its quarantine was when a passenger, who had disembarked from the ship in Hong Kong on February 1, was tested positive for COVID-19. After two days, that is on February 3, the cruise was quarantined in Japanese water. Over a month, more than 700 people on board were found to be COVID-19 positive, which included a nurse.

Scientists and researchers took the opportunity to glean information about the novel coronavirus, mainly how easily the virus spreads, estimation of the disease’s severity and also to find out how many affected people go without symptoms.

John Ioannidis, an epidemiologist at Stanford University in California, says, “Cruise ships are like an ideal experiment of a closed population. You know exactly who is there and at risk and you can measure everyone.”

Percentage of Infected People Without Symptoms

Japanese officials conducted over 3,000 tests on the passengers of the cruise ship, prioritising the elderly ones and those displaying symptoms. Some passengers were even tested more than once so that the viral spread over time could be understood better.

The data out of the extensive testing was analysed by a collaborating team from Japan and UK led by Kenji Mizumoto. They published their results in the journal Eurosurveillance, where they reported that over 18% of the infected people did not have any symptoms. This is a significant number. The asymptomatic cases are especially dangerous for the elderly people. Because an asymptomatic infected person might transfer the infection to an elderly person or to a person who is immunologically not very strong.

This result shows the necessity of more and more testing for COVID-19.

Disease Severity

Another team led by Timothy Russel, a mathematical epidemiologist at the London School of Hygiene and Tropical Medicine attempted to estimate the case fatality rate (CFR), the proportion of deaths out of confirmed cases. They published their data in the preprint archive medRxiv, which stated that the CFR in China was way below what WHO predicted. It was 1.1%, while WHO estimated it to be 3.8%.

This difference in estimation was due to the denominator. WHO simply divided China’s total number of death by total number of infected people that were confirmed to have the infection. This method does not consider that only a fraction of the total infected people have been tested.

Russel’s team took the data from the cruise ship where almost everyone was tested and then extrapolated it to the situation in China. This, according to them, makes the estimation more robust.

Russel’s team also estimated the IFR (Infection Fatality Rate) for China. The IFR signifies the total infection, including the asymptomatic ones that could result in death. The IFR goes even lower, 0.5%.

Marc Lipsitch, the infectious-disease epidemiologist at the Harvard T.H. Chan School of Public Health in Boston says, “The IFR is an important indicator to help public-health officials understand disease severity and how to intervene.” Regarding the work of Russel and his team, Lipsitch says, “This is an important effort, but one important caveat is that the infections were ascertained by viral testing and might have missed people who had been infected but recovered.”

Ease of Spread of the Virus

Again, a joint study between Kenji Mizumoto of Japan and Gerardo Chowell of USA was conducted to look for the spread of the virus and how the quarantine measures reduced it. Published in Infectious Disease Modelling, their estimation said that before quarantine one person could infect seven others. The high infection rate was probably due to the close environment of the ship where hundreds of passengers touched surfaces contaminated with the virus. But after quarantining it dropped down to below one, meaning one infected person now could infect less than a person.

Also watch: Over 340,000 COVID-19 Infection Cases Reported Globally