GlobalData has produced three-scenario peak-week models for all countries experiencing more than 100 cases of the new coronavirus disease 2019 (Covid-19). While the peak-week models fit the epidemiology curves in markets such as the US and Western Europe, several Asian countries do not fit the expected exponential curves of a typical epidemiology outbreak in an immune-naïve population. GlobalData’s epidemiology team used its experience in modelling the global Covid-19 outbreak to examine the factors causing Asian countries to have different outbreak trajectories and produced an alternate forecast model for Japan. One-size-fits-all recommendations to counter the outbreak will not be effective, as the pandemic is showing different outcomes in each country. Governments need to tailor solutions to their own unique situations.

Japan’s Covid-19 case count and infection rate have been relatively mild since its first reported case on 16 January. Given the country’s proximity to China, large numbers of travel and commercial contacts within Asia, and having the infamous Diamond Princess cruise ship in its harbour, the rate for total infections in Japan was as low as one case per million population one month later in February, and seven cases per million population two months later in March. For comparison, the first suspected domestic transmission in the US occurred on 26 February. The rate for total infections one month later in the US was already at 255 cases per million population, and a staggering 2,946 cases per million population two months later.

Figure 1 presents Japan’s historical data of daily new cases plotted against general transmission risk models. New viral infection with R0 higher than one and moderate severity in the majority of cases, such as the novel coronavirus, would be expected to spread rapidly after being introduced into an immune-naïve population. The general transmission risk models follow this expectation. Countries like the US, Italy, and Spain experienced this type of trajectory, with cases in these markets doubling every two to five days during the first few months of the outbreak. However, this scenario did not play out in Japan because of the fast, strong, early countermeasures that were taken. Japan responded extremely rapidly in the beginning stages of the Covid-19 outbreak, likely due to its experience with past viral outbreaks such as severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS), as well as the nation’s general hygiene practices and citizens’ tendency to wear masks when out in public.

Japan started seeing a concerning increase in the number of cases by end of March, and the government declared a limited state of emergency on 7 April in the most hard-hit areas. The declaration was expanded to the country as a whole on 17 April when cases continue to climb. It is unclear what caused the second surge in cases, but it is likely due to a combination of uncontrolled imported cases, undetected domestic transmission, and failure to meet testing demands. Unlike South Korea, testing in Japan was not scaled up to the general public and only limited to those fitting specific criteria.

However, GlobalData has already seen a significant downturn in new daily cases since the national emergency was declared. Figure 1 also shows GlobalData’s forecast for Japan’s trajectory in the next several weeks. GlobalData expects Japan to quickly stamp out this recent surge in cases, but the country is likely to see additional surges in the future.

Figure 1: Japan, Covid-19 Epidemiology Forecast for Trajectory of Daily New Cases (N)