While the state of emergency for the new coronavirus outbreak is lifted in some parts of Japan, there are reports that warn of another outbreak. A University of Tokyo study indicates that if curbs on people’s activities are relaxed, the number of cases will rapidly increase in about one month. A University of Iowa report warns that a “second wave” of infections will occur if limits on movement are not maintained for a period of time. It seems that some restraints on activities will be necessary to prevent another outbreak while resuming economic activity.
University of Tokyo associate professor Jun Ohashi estimated the increase in infections if requests to stay home are lifted.
The University of Tokyo study assumed a city with a population of 100,000. The effective reproductive number, which is the number of people infected by one infected individual, was set at 2.5. In the study, when restrictions were implemented at a point when there were 50 cases, the number of cases then fell for the moment. When the restrictions were lifted 60 days after its implementation, the number of cases reverted to 50 people in 30 days. The study results showed that in a city of 10 million people, the number of cases reverts to its previous value 30 days after restrictions are lifted.
According to Ohashi, if the state of emergency is lifted in Tokyo and Osaka on May 31 and people will be free to go outside, the period of restriction will be less than 60 days. In that case, it may be less than 30 days before the number of cases returns to the number before the state of emergency was declared.
Foreign universities have released similar reports. A research team at the University of Iowa submitted a report to Iowa state authorities in April 2020. The report says that it is highly possible that a second wave of infections will occur if restrictions are lifted within four months and people return to normal daily activities.
A research team at Imperial College London estimates that the outbreak may recur from fall to winter 2020 if U.K.’s preventive measures are relaxed in September 2020. Even if school closures and stay-at-home restrictions are successful, a second wave may occur because the population will not have acquired herd immunity.
In countries that have removed lockdown measures, the number of infections have risen again. Germany’s effective reproductive number increased from 0.65 to greater than 1 after the government eased its restrictions, according to the Robert Koch Institute, the German government’s public health institute. An effective reproductive number greater than 1 indicates that the infection is spreading.
A cluster of infections developed in Seoul, South Korea, among people who went to a nightclub after the stay-home restrictions were eased. New cases have been found in Wuhan, Hubei Province, China, after the removal of the city’s lockdown.
It seems that limits on activities need to be maintained in order to prevent another outbreak. The University of Tokyo study says that the number of cases may be reduced even if the state of emergency is lifted, on the condition that probability of infection is reduced by 60 to 70% by such measures as reducing social contact.
The University of Iowa report suggests that second wave may be prevented if there are limits on activities with a high infection rate, such as large gatherings, and protective gear such as face shields are used effectively.