A recent study by Japanese researchers found that most COVID-19 patients with no symptoms (asymptomatic) will stay that way – researchers from Fujita Health University Okazaki Medical Center in Aichi Prefecture, Japan, studied some 128 asymptomatic coronavirus patients who were aboard the much-talked-about Diamond Princess cruise ship; these included 96 passengers who tested positive for the coronavirus but had no symptoms and 32 of their others who tested negative.

“In this cohort, the majority of asymptomatic infected persons remained asymptomatic throughout the course of their infection,” said Dr. Yohei Doi, of the Department of infectious diseases at Fujita Health University.

According to the study, asymptomatic coronavirus patients tend to recover within a minimum of nine days of having their infections confirmed via polymerase chain reaction (PCR) tests. Nearly half of the patients were cleared of the virus within nine days after first testing positive for COVID-19, while 90% of people recovered within 15 days. The researchers further explained that the 11 patients who did develop symptoms later had been pre-symptomatic, rather than asymptomatic for COVID-19. While most asymptomatic patients were unlikely to recover within five days after the initial positive test, they would “be cleared of the virus” after eight to 10 days.

The findings also showed that the time it took to recover from the coronavirus infection increased with age.

Based on this, the Japanese health ministry has revised its guidelines for hospitalisation 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. The health ministry also shortened the time of quarantine for coronavirus patients from 14 to 10 days.

“Repeating PCR tests in patients with positive test results is meaningless soon after the initial diagnosis, as the test results will remain the same and as a result the resources won’t be used effectively,” Doi said. “Our study has also proven that the amount of virus decreases significantly within that period, which makes the odds of transmission after long-course infection very low.”

The findings are a stark contrast to the ongoing debate on the transmission of the coronavirus by asymptomatic patients. Earlier in June, the World Health Organization (WHO) sparked controversy over coronavirus transmission routes when a top official said that such transmission is “very rare” – Maria van Kerkhove, head of WHO’s emerging diseases and zoonosis unit, later noted that there is not enough data to conclude how infectious asymptomatic carriers are.