A man who arrived at Narita International Airport on a flight from Shanghai receives an explanation about self-isolating as a measure against the new coronavirus, in Narita, Chiba Prefecture, east of Tokyo, on March 9, 2020. (Mainichi/Koichiro Tezuka)

TOKYO -- An expert is warning of a second wave of novel coronavirus infections in Japan due to a surge in infected people returning to the country from overseas.

Since the beginning of March, the number of new infections has hovered around several dozen per day, but the number of infected people returning to the country from overseas has risen markedly, accounting for nearly 30% of the infections reported in Japan between March 17 and 23.

Over the past two weeks, more than 110 people in Japan who had traveled overseas were confirmed to have been infected.

"Infections in Europe, the United States and in Southeast Asia are increasing. A number of infected people beyond comparison with the number in China to date will come to Japan," Hiroshi Nishiura, a professor of infectious disease epidemiology at Hokkaido University, told reporters on March 19 following a government expert panel meeting. Nishiura is part of a team operating under the Ministry of Health, Labor and Welfare to address clusters of infections with the novel coronavirus. Repeating such warnings during the news conference, he said that Japan could see a major spread of infections if it approached the situation without sufficient precaution.

The first novel coronavirus infection in Japan was reported in mid-January. A total of 13 people who were found to have stayed in the Chinese city of Wuhan, the source of the global virus pandemic, were subsequently found to be infected. After that, other infected people who had returned to Japan from China or who were visiting Japan are thought to have carried the virus into the country.

However, the spread of coronavirus disease cases subsequently began to decrease in China, and flare up in other countries. Including people who were found to be infected during airport quarantine checks in Japan, between March 10 and 16, a total of 31 people who had been overseas were found to have been infected, accounting for roughly 10% of the total number of new infections. But between March 17 and 23, the number rose to 87, accounting for about 29% of all new infections.

Since cases of COVID-19, as the novel coronavirus disease is formally known, began to spread around the world, the Japanese government has stepped up border control measures. These include testing all Japanese citizens returning from areas from which foreigners currently cannot enter Japan, and having people from China, South Korea, Iran, Egypt and countries in Europe observe a 14-day self-isolation period and refrain from using public transportation. The same measures will be applied to people arriving from the United States from March 26.

However, some people returning from countries in Southeast Asia and Central and South America that have reported relatively few infections, such as Vietnam and Mexico, have also been infected with the virus.

Koji Wada, a public health professor at the International University of Health and Welfare, commented, "Even in countries where the data says infections are not rising, traveling overseas increases the risk of infection. Elderly people should avoid unnecessary travel, and those who have been overseas should refrain from going outside."

(Japanese original by Sooryeon Kim, Lifestyle and Medical News Department)