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COVID-19 patients with no symptoms likely to stay that way: Japanese researchers

Jun 15, 2020 (Japan Times) - What are the odds COVID-19 patients with no symptoms could later develop them?

Quite slim, according to a recent study led by a group of researchers in Aichi Prefecture, who have discovered that asymptomatic coronavirus patients tend to recover within nine days of having their infections confirmed via polymerase chain reaction (PCR) tests.

The findings, involving a study on how the disease developed in 90 people without symptoms who contracted the disease aboard the Diamond Princess cruise ship, were published Friday in the New England Journal of Medicine and showed that only 11 people without symptoms would go on to develop them later.

“In this cohort, the majority of asymptomatic infected persons remained asymptomatic throughout the course of their infection,” a team led by Yohei Doi, a doctor and professor of the department of infectious diseases at Fujita Health University wrote in the report.

The results showed that nearly half of the patients were cleared of the virus within nine days after first testing positive for COVID-19, while 90 percent of people recovered within 15 days. The findings also showed that most patients were unlikely to recover within five days after the initial positive test.

Based on the findings, the health ministry on Friday revised its guidelines for hospitalization of COVID-19 patients. It is now advising that patients who test negative twice over six days after the initial positive test should be discharged.

Fujita Health University’s Okazaki Medical Center took in 128 people from the virus-hit Diamond Princess — 96 passengers who tested positive for the coronavirus but had no symptoms and 32 of their cabinmates who tested negative. All were between the ages of 9 and 77. In total, data on 90 patients without symptoms were available for analysis.

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Japan’s World Cup campaign ended in the cruelest possible fashion on June 29, as Gabriel Martinelli scored in the fifth minute of stoppage time to give Brazil a 2-1 victory over the Samurai Blue in their knockout match in Houston. Japan had led in the first half and were still level at 1-1 in the final moments, but Martinelli’s late strike sent Brazil into the Round of 16 and eliminated Japan from the tournament.

Strong earthquakes have continued to shake parts of Japan in recent weeks, with 11 temblors measuring lower 5 or above on the Japanese seismic intensity scale recorded across the country since April 2026.

A Kintetsu Railway train derailed inside Kyoto Station on the morning of June 29, forcing partial suspensions on the Kintetsu Kyoto Line for the rest of the day and causing long delays that hit commuters, students and tourists.

A section of stone wall at Hikone Castle, one of Japan’s few surviving original Edo-period castles and a National Treasure whose main keep remains intact more than 400 years after its construction, collapsed after heavy rain caused by Typhoons No. 7 and No. 8, Hikone city officials said.

Japan advanced to the knockout stage of the World Cup after a 1-1 draw with Sweden on June 25, finishing second in Group F and setting up a Round of 32 clash with Brazil in Houston.

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