Q&A about Novel Coronovirus (For the General Public)

April 4, 2020

6  Incubation Period  


Q25  How long is the incubation period (can it be transmitted during this time)?  (UPDATED)

According to the World Health Organization (WHO), the incubation period is currently 1-14 days (generally 5 days), and based on information on other coronaviruses, it is recommended that infected people’s health be monitored for 14 days.


Q26  What was the way of thinking on which those who returned by charter flight from Wuhan or who disembarked from the Diamond Princess were allowed to return home?  (UPDATED)

According to WHO's findings, the incubation period is currently 1-14 days (generally 5 days). Based on information on the coronavirus up to now, it is recommended to observe the health conditions of uninfected individuals for 14 days.  In addition, among the returnees of the charter flights, only 5 of the 829 persons who had a negative PCR test immediately upon return to Japan later had a positive PCR test.


Regarding passengers on the Diamond Princess cruise ship, measures were taken to prevent the spread of infection by separating into private rooms as of February 5, and based on the expert knowledge of the WHO and knowledge about tests on the people who returned by charter flights, and the Quarantine Law (Law No. 211 of 1951), after the 14 day quarantine period was completed on February 19, those who tested negative using the PCR test during that period and who had no problem after further health checks, were allowed to disembark.


In addition, for those who started disembarkation on February 19, as a precautionary measure and as follow up, regular health checks were carried out after disembarkation and they were asked to refrain from going out unnecessarily for two weeks.    On March 15, a 14-day health observation period was completed on board the ship, and the health follow-up for the 1,011 people who had disembarked between February 19 to 23 was completed.

Q27   Why are there positive cases (Japan, US, Australia, etc.) after disembarking from the cruise ship?

After disembarking the cruise ship, there are several possible factors that have lead to positive infection.  For example, they may have tested “negative” because at an early stage, there is not enough virus in the body to be detected by the test.  Afterwards, the virus may have increased so that when re-tested, it was found to be “positive”.