新型コロナウイルス感染症の流行と疫学的解析について（その1）

抄録

On 5th January 2020, World Health Organization notified all member states about the new outbreak of pneumonia of unknown cause in Wuhan City, Hubei Province of China. It was a beginning of pandemic of the novel transmissible disease, which was later named as COVID-19. The causative agent was soon searched using whole genome analysis and a new coronavirus that is very similar to the virus causing SARS was identified. The virus was named SARS-CoV-2. COVID-19 rapidly spread inside China and the Government of China decided to shut all public transportation at the end of January. In Japan, a man who travelled back from Wuhan city in early January was the first case. To rescue Japanese nationals trapped in Wuhan, the Japanese Government chartered five flights. All passengers were put under quarantine after arrival and were subjected to PCR testings. On 1^st February, a passenger on a cruise ship ‘Diamond Princess’ that had departed from Yokohama was confirmed to be infected with SARS-CoV-2 at Hong Kong. Therefore, all passengers and crews on the ship were put under quarantine offshore Yokohama, the final destination of the cruise. PCR testings were performed on symptomatic persons and persons that had close contact with cases. The number of cases increased day by day from the start of the quarantine. Epidemiological research was conducted worldwide from an early stage and demonstrate good indices to understand epidemiology of COVID-19. Case reports from China showed presence of many asymptomatic cases especially in younger generations. Mathematical modelling studies estimated the length of incubation period of COVID-19 and its serial interval and the possibility of transmission during asymptomatic period was also highlighted to give warning. Effectiveness of the quarantine measures on the Diamond Princess was evaluated in another study and drastic reduction of the predicted number of future cases was proven. At the end of February, a specialist advisory group was organized under the Ministry of Health, Labor and Welfare. Advised by this group, Japan started to tackle COVID-19 by applying a unique strategy in the world.