May18, 2020

COVID-19 Tokyo vs NYC: Slower infection gave Tokyo time to prepare


Since the middle of March when the U.S., especially New York City (“NYC”), started facing rapid growth of COVID-19 cases and deaths, we saw various international media outside Japan argued that Tokyo would face similar situation like NYC sooner or later. Some Japanese doctors working at hospitals in NYC posted strong warnings in Japanese mass media and SNS. It seems such concern was reinforced by the several factors; Japan never implemented lockdown, the number of PCR tests has been significantly lower than other countries, and the speculation that Japan government might have wanted to conceal the problem trying not to affect Tokyo Olympic Games (which was announced to postpone on March 24th).

Almost 2 months passed since then, it seems that Tokyo, as well as Japan as a whole, has been managing the pandemic with significantly lower fatalities compared to NYC and western Europe countries.

In this report, we compare historical data of COVID-19 fatalities and cases in Tokyo and NYC, trying to answer below questions.

  • How the speed of COVID-19 infection spread in Tokyo and NYC has been different.Did Tokyo ever face situation where it was reasonable to worry about the possibility to become like NYC?
  • Do we observe any impact of actions by Tokyo/Japanese government on the speed of infection spread?
Comparison of Tokyo and New York City

First of all, here are log-scale charts comparing deaths and confirmed cases in Tokyo and NYC. As you can see, Y-axis is shown as log-scale of 2 (2, 4, 8, 16, 32, 64…). If you show them in normal linear chart, the chart becomes exponential curve because infectious diseases spread with exponential growth. The problem of exponential curve is, the line gets steeper and becomes almost vertical. Visually it is difficult to understand how the speed of pandemic spread is different between Tokyo and NYC, or how the speed has been changing.

Log-scale chart is useful to understand the big picture and compare different countries/cities.
Chart 1: Total Deaths in log-scale
Chart 2: Total Confirmed Cases in log-scale

Here are some insights from these charts.  During first 2 to 3 weeks from the first confirmed case or death reported, the pandemic spread in NYC much faster than Tokyo. Tokyo has never faced such high speed of spread like NYC since the first case up to today.

- Chart 1: Total number of deaths in Tokyo was 189 as of Day 76 (May 11th, 2020). NYC surpassed this number on Day 12 (March 15th, 2020). 4 weeks after the first death was reported, NYC and Tokyo reached total death of 6,166 and 5 respectively.

- Chart 2: Total number of confirmed cases in Tokyo was 4,886 as of Day 109 (May 11th, 2020). NYC surpassed this number on Day 17 (March 20th, 2020).

While we can get big picture from above charts, we can do deep-dive analysis by measuring the estimated growth of deaths and confirmed cases. We calculated “estimated number of days to double” and illustrated in below charts.

Let’s say, we would like to measure the estimated growth rate of total deaths back around April 1st.  We take two data points: total deaths until April 1st and until March 25th (7 days before April 1st) respectively. Based on the increase for 7 days, we made estimate calculation that “Around on April 1st, the total death was growing double in X days”. Please refer to Appendix for our calculation formula.

Chart 3: Number of days for total death to double|305-3&graph_index=0&graph_type=line&graph_data_from=18-3-2020&graph_data_to=17-5-2020

Here are some insights we can find from these two charts:

- In Tokyo, the rate of growth was the highest between around March 29th and April 6th in terms of both total deaths and total cases, which was around “doubling in 4 days”. The total death and confirmed cases as of April 6th was 30 and 1,115 respectively. After April 7th, the growth rate kept going down. As of May 11th, growth rate of total death and total cases are “doubling in 21 days” and “doubling in 100 days” respectively.

In NYC, the rate of growth for first 3 weeks was “doubling in 1 – 3 days”, much faster than Tokyo. The growth rate of total deaths in NYC slowed down to “doubling in 4 days” (which was the highest rate in Tokyo) around on April 3rd, 3 weeks after the first death reported.  Total deaths had reached 3,466 at that point. The growth rate in NYC has been slowing down continuously. As of May 8th, the growth rate of total death and total cases are “doubling in 101 days” and “doubling in 105 days” respectively.

Impact of government actions and other factors

In this section, we take a closer look at how growth rate in Tokyo has been changing in the context of actions by Japanese Government as well as Tokyo Metropolitan Government.

Here are key moments in Tokyo/Japan related to COVID-19, which may have affected people’s mindset and behavior.

Jan 24th: the first confirmed case in Tokyo

Feb 5th: 10 cases reported at Diamond Princess cruise ship at the port of Yokohama

Feb 25th: Cluster Response Team was established in the Ministry of Health, Labor and Welfare

Feb 26th: the first death case in Tokyo

Mar 23rd: Tokyo Governor Ms. Koike held press conference and requested citizen to follow “the three Cs” social distancing for 3 weeks.

Mar 24th: National government and IOC announced postponing Tokyo Olympic Games.

Mar 29th: A well-known comedian passed away in Tokyo due to COVID-19.

Apr 7th: National government announced “State of Emergency” for 7 prefectures including Tokyo (and it further expanded to all across Japan on Apr 16th).

Here’s “Number of days to double” charts again by mapping these key moments.

Chart 5: Number of days for total death to double (only Tokyo)

Chart 6: Number of days for total cases to double (only Tokyo)

From both charts, we can observe that rate of doubling death/cases were accelerating until the end of March, and it started to slow down gradually around from April 7th, when National Gov announced state of emergency.  Since it takes around several days to 1 week on average for COVID19 symptom appears, we may estimate that people’s behavior may have changed around last week of March.

Therefore, we can deduce that Tokyo Governor Koike’s press conference on March 23rd, together with postponement of Tokyo Olympic Games on March 24th, may have had influence on people’s behavior, although such correlation doesn’t prove the direct causality.

Appendix – how to calculate number of days to double

The number of days for which total confirmed cases became double is calculated as follows.

For example, total confirmed cases in Tokyo was 1,914 on Day 32 and 897 on Day 25 (change in 7 days). In this case, we can calculate that

It means, based on data last 7 days, the total confirmed cases has become double in 6.4 days.

Report written by:

Contributing Analyst 

Akira Morita