Epidemiological Tools that Predict Partial Herd Immunity to SARS Coronavirus 2

Yasuhiko Kamikubo; Atsushi Takahashi

is likely that the L type took over the S type because of higher replicative potential and/or faster transmission. Asymptomatic ratio of Japanese nationals evacuated from Wuhan, who are more likely to be infected by the L type, is 30.8% (95% confidence interval: 7.7-53.8%). 6 In contrast, 51.4% (318/619) of RT-PCR confirmed cases among passengers in the cruise ship Diamond Princess, an outbreak traced to a Hong Kong passenger who is most likely to have S type virus, were asymptomatic (https://www.niid.go.jp/niid/en/2019-ncov-e/9417-covid-dp-fe-02.html). Although the subtypes of the virus remain to be clarified, the higher asymptomatic ratio among cruise ship passengers supports the view that infection by S type is more likely to be asymptomatic than that by L type and easier to avoid recognition by surveillance systems.