  This study analyzed the spread and decay durations of the COVID-19 pandemic
in different prefectures of Japan. During the pandemic, affordable healthcare
was widely available in Japan and the medical system did not suffer a collapse,
making accurate comparisons between prefectures possible. For the 16
prefectures included in this study that had daily maximum confirmed cases
exceeding ten, the number of daily confirmed cases follow bell-shape or
log-normal distribution in most prefectures. A good correlation was observed
between the spread and decay durations. However, some exceptions were observed
in areas where travelers returned from foreign countries, which were defined as
the origins of infection clusters. Excluding these prefectures, the population
density was shown to be a major factor affecting the spread and decay patterns,
with R2=0.39 (p<0.05) and 0.42 (p<0.05), respectively, approximately
corresponding to social distancing. The maximum absolute humidity was found to
affect the decay duration normalized by the population density (R2>0.36, p
<0.05). Our findings indicate that the estimated pandemic spread duration,
based on the multivariate analysis of maximum absolute humidity, ambient
temperature, and population density (adjusted R2=0.53, p-value<0.05), could
prove useful for intervention planning during potential future pandemics,
including a second COVID-19 outbreak.
