Only 0.1 percent of people in Tokyo tested positive for antibodies against the coronavirus, a survey conducted by the health ministry found Tuesday, indicating the spread of the virus in Japan’s capital remains limited, even though the number of cases may be higher than those already found.
The survey involved 1,971 participants in Tokyo. By limiting testing for the virus, an approach said to help prevent the spread of the disease, Japanese authorities have left many wondering what the true infection rate in the country is. If the sample in Tokyo is representative of the general population, it would mean around 14,000 cases in the capital, compared to the more than 5,000 cases identified so far.
The antibody results, which indicate exposure to the virus, are far lower than those seen in the Western cities and countries that became hot spots in the global pandemic. A surveillance study carried out for the U.K. suggested 17 percent of residents in London had COVID-19 antibodies, based on results announced May 22, while on the same day in New York, antibody tests found 20 percent of the population was positive. Spain had a 5 percent positive rate in antibody tests conducted in May.
Japan also conducted antibody tests in Osaka, where a 0.17 percent positive rate was recorded among 2,970 people, and Miyagi Prefecture, where the rate was just 0.03 percent of 3,009 people surveyed. Samples were collected from a total of about 8,000 people in the three regions.
The figures are notably higher than the ratio of 0.015 percent based on the 18,261 people who have been confirmed to be infected with the virus in Japan by Monday, out of the country’s total population of roughly 125.9 million.
The discrepancy shows a large number of infections have gone undetected, with people either recovering without being tested or showing no symptoms.
The surveys were conducted between June 1 and 7, targeting residents aged 20 and above, and required antibodies to be identified by two separate tests made by Roche Holding AG and Abbott Laboratories for the result to be considered positive.
Health Minister Katsunobu Kato told a news conference that the government will further study how to utilize the latest survey and also conduct more antibody tests to estimate how many people could become infected if a second wave occurs and how many would need vaccination.
The ministry cautioned that the latest tests could not determine the nature of the antibodies, such as how long they remain in the body, or whether the presence of antibodies protects people against being infected again.
In the largest antibody test undertaken so far in Japan, Softbank Group Corp. found 191 cases among 40,000 employees, family members and medical workers. The result was a positive test rate of 0.43 percent, with only eight of more than 19,000 workers at its stores having been in contact with the virus.
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