Commuters wearing masks near Shinjuku Station in Tokyo on Friday. The metropolitan government decided to shift its Tokyo Alert to the third stage, permitting pachinko parlors, karaoke bars and amusement parks to be opened. Photo: AFP / The Yomiuri Shimbun

The decision by the Metro Government in Tokyo to lift its restrictions followed seven days with the average number of cases below 20, with more than half the cases being traced to known clusters.

The lifting is in stages starting with restaurant hours extended first. Karaoke studios’ restrictions end June 19.

The lifting also comes 66 days after a partial lockdown was declared nation-wide on April 7.  So how has Japan’s Covid-19 situation been during these 66 days?

First chart: new cases, patients hospitalized

The blue line shows the number of new cases per day, which peaked at 743 cases on April 12. The recent seven-day average nationwide has been fewer than 40 new cases.

The green area shows the number of people with symptoms, which peaked in early May, but those subjective data were replaced by more concrete data on the number of patients hospitalized, shown in the brown area.

On June 11, the number of those hospitalized dropped below 1,000 for the first time. Of the 17,292 cases reported to date, 15,383, or 89%, have been discharged. 

Reported Covid-19 fatalities totaled 920, or 5.3%, on June 11, but the actual number may be more than 1,000 based on nationwide mortality statistics.

Second chart: testing, positivity rate

Polymerase chain reaction tests now average about 3,000 per day and the coverage has reached 261 per 100,000 population, which still remains low compared with peer nations. 

But importantly, the percentage of tests proving positive has declined from a high of almost 9% in April to 5.4% this past week. This positivity data is shown in the blue line below.

Third chart: compound daily growth rate of new cases

The chart below shows the speed at which the pandemic is spreading. We calculate the speed using the formula [ (X/Y)^(1/7)-1] where X is today’s case number and Y is the week-earlier number.

Back in February, the pandemic was growing at a compound daily growth rate of more than 16%, which at the time was faster than the growth rate in the US. The growth rate is now down to 0.2% per day versus about 1.3% per day in the US. The pandemic is hardly growing in Japan.

Fourth chart: effective reproduction number

So how many people does one carrier of the virus infect? In the days before the April 7 lockdown, the rate of reproduction was more than two persons per carrier and the pandemic was spreading.

Recent data shows the reproduction rate spiked in early June due to clusters in Kita-Kyushu and in-hospital transmissions elsewhere. But the situation now appears to be in better control.  

The reproduction rate has dropped to 0.866. A rate below one indicates the pandemic is dying off, while a rate above one indicates further spreading.

So recent statistics suggest the pandemic may be ending in Japan. But cases can still spike like those in Kita-Kyushu and the government is recommending continued caution.

A retired Tokyo-based analyst for a major US investment bank, Matt Aizawa now crunches numbers beside a lake north of the city.