The Olympic rings in front of the National Stadium, the main stadium of the Tokyo 2020 Olympics and Paralympics, at Japan Sports Olympic Square in Shinjyuku Ward, Tokyo, on May 24, 2021. Photo: AFP / Kazuki Wakasugi / The Yomiuri Shimbun

The US CDC has raised its COVID 19 risk appraisal for Japan from Level 3 to Level 4 meaning “Travelers should avoid all travel to Japan.”

Japan now joins the ranks of other Level 4 countries such as Canada, Germany and Russia and leaves the Level 3 group including Iceland, Thailand and UK, to which CDC recommends “Travelers should avoid all nonessential travel.”

For travelers to Level 2 countries such as Ghana, Singapore and Korea, the CDC recommends “Travelers at increased risk for severe illness from COVID 19 should avoid all nonessential travel.”

There are only 29 countries and regions appraised Level 1 including Australia, China, Hong Kong, Taiwan and New Zealand.

Mathematical Methodology

The CDC’s mathematical model for classifying countries and regions is simple and straight forward.

It first checks whether the PCR testing regime is robust or not: How many tests have been conducted per 100,000 population over the previous 28 days?

An aggregate of over 13.7 million PCR tests have been conducted to date and for the most recent 28 day period, over 1,800 tests per 100,000 pop have been recorded.

The CDC ranks these figures into four categories: the best category is more-than-1,200 test per 100,000, followed by 401-to-1,200, then 200-to-400 and less-than-200 tests. Japan fits the best category here.

Test-to-Case Ratio

Next the CDC examines the test-to-case ratio. Last summer, Japan conducted over 100 tests per case uncovered during a 28 day period. The ratio is now down to about 15.

The CDC ranks these figures into three categories: The best group has performed more than 30 tests per case uncovered. The middle group is from 10-to-30 tests and then there are those with less-than 10 tests. Japan ranks in the middle group here.

Incident Rate

The CDC finally looks at the number of new cases over the previous 28 days per 100,000 population.

There is one criterion for small regions with fewer than 200,000 people and another one for regions with over 200,000 people, which would be the one used for Japan with a population over 126 million.

The CDC classifies the data into four levels: Regions with less-than-5 would be classified as Level 1. Japan would have been classified as Level 1 last summer.

Regions or countries with 5-to-50 cases are classified as Level 2.  Japan would have been Level 2 until December last year when it deteriorated to Level 3. By the beginning of May the incident rate was already indicating Level 4.

Most Recent Reproduction Rate

So what is the outlook for the Olympic Games? Here is another chart to consider.

In the above chart, the blue line is the reproduction rate: How many people are getting newly infected by those known to be infected at this time.

When the reproduction rate is 1.2, it means ten people are infecting twelve and the pandemic is expanding. The rate recently dropped to less than 0.9 meaning the pandemic is in a contraction phase…for the time being.

The gray columns show incidents of long weekends with a holiday on either Friday or Monday. It also includes weekends with a holiday on either Tuesday or Thursday when people are likely to take a day off.

The red arrows indicate instances where such long weekends were followed by a jump in the reproduction rate. The most recent long weekend was the Golden Week which was predictaby followed by the spike.

The spike in the reproduction rate in April coincides with reported cases of more contagious variants from abroad, although we should note that coincident does not mean cause.

We are now entering a period in Japanese calendar when there are no long weekends until late July right before the Olympic Games indicated here with an orange column.

That plus the partial lockdown declared in various regions may do the trick. Hopefully the much criticized glacial pace of vaccination may pick up in coming weeks. But very few are holding their breath and most Japanese want the games canceled.