Antibody tests for the novel coronavirus suggest a 0.1 percent infection rate in Tokyo, health minister Katsunobu Kato said Tuesday, as the government seeks to better grasp the scale of the pandemic's spread in Japan.
The health ministry earlier this month began testing for coronavirus antibodies in Tokyo as well as in Osaka and Miyagi prefectures. The positive rates for Osaka and Miyagi in the country's west and northeast were 0.17 percent and 0.03 percent, respectively.
Samples were collected from a total of about 8,000 people in the three regions. The presence of antibodies indicates a person has been infected with the virus, regardless of whether the person developed symptoms.
The results show only a very limited spread of the virus and, while different testing kits can yield different results, they compare with positive rates of some 20 percent detected in antibody tests in New York City and 5 percent in Spain.
But the figures are still notably higher than the 0.015 percent infection rate based on the 18,261 people confirmed to have caught the virus in Japan as of Monday out of the country's total population of roughly 125.9 million.
That figure is mostly based on the polymerase chain reaction test used to determine whether someone is currently infected with the virus. The discrepancy shows a large number of infections have gone undetected with people either recovering without being tested or showing no symptoms.
New infections in Tokyo have been rising in recent days. The Tokyo metropolitan government on Monday confirmed 48 new coronavirus infections, up one case from the previous day, marking the biggest daily increase since May 5 for the second straight day.
On Tuesday, the number was 27, which brought the total of COVID-19 cases in the capital to 5,619, the highest among the country's 47 prefectures, according to officials.
The number of new cases has been on an upward trend since a nationwide state of emergency was fully lifted on May 25 and the metropolitan government thereafter eased restrictions on social and business activities.
By prefecture, the rate of confirmed infections to population was 0.038 percent in Tokyo, 0.02 percent in Osaka, and 0.004 percent in Miyagi.
The government plans to conduct an analysis of the antibodies at the National Institute of Infectious Diseases as it remains unknown how long they last in a person's body and whether they can protect a person from becoming infected again.
"We'd like to consider measures for utilizing antibody tests and (holding) further antibody surveys," said Kato.
The health ministry conducted the survey between June 1 and 7, targeting residents aged 20 and above. It aimed to estimate how many people could become infected if a second wave occurs and how many would need vaccination.
The ministry initially sought to collect samples from 10,000 people in total.
As of Tuesday, the total number of infections in Japan had exceeded 18,300, including about 700 from the Diamond Princess cruise ship that was quarantined in Yokohama in February. The country's death toll from COVID-19 stood at 951.
In Japan, antibody tests have also been conducted in the private sector and by sports organizations, including the Japan Sumo Association.
SoftBank Group Corp. has tested some 44,000 people, including its employees and medical workers, with 0.43 percent found to be positive.
The rate was 1.79 percent among medical workers and 0.23 percent among employees at SoftBank group companies and their clients.
It also showed some had antibodies despite having tested negative in the PCR test