A hypothesis and verifiable analysis on the impact of social distancing and BCG vaccination on COVID-19 (as of Mar. 28th)

I write this article only because I hope the pandemic of COVID-19 becomes somewhat manageable and minimize the negative impact on the whole world. 

I'm not a medical specialist, but just want to share a point of view which may explain this pandemic situation and give some implication on action items to be taken in each country.

What I did is very simple, I just combined the two excellent analyses conducted by my ex-colleagues. The originality of the analysis below totally comes from their outstanding talents, not me.

Firstly I would like to review their hypotheses. Eisuke's report shows the impact of social distancing in the early stage.(updated here) He says when to convene the national “social distance” policy matters. It clearly explains why Italy, Spain and Iran have got worse, by calculating the #(number) of confirmed deaths per capita.

Jun's report shows BCG vaccination may strengthen immune to the novel coronavirus. He gives us five reasons that support the hypothesis. It clearly explains that "the spread speed is fast in Western Europe and the U.S. while the spread speed among Russia, eastern European countries, and Asian countries except Wuhan city is slow."

Secondly I would like to share my thoughts inspired by those two fabulous analyses. 
・If we combine these two hypotheses, it may explain the coronavirus situation well and give us some implication on action items to be taken in each country.
・The analysis should be verifiable in order for any of us to verify its validity and evolve these hypotheses.
・Data sources should be open and easy to access, and the process of analysis should be kept as simple as possible.

Thirdly I go into details of the analysis by showing the definition of each parameter and the data source that I use.
・I take "the number of deaths per capita because of the disease" as the key indicator for the same reason as described in Eisuke's report.
・I pick up the top 20 countries in terms of # of confirmed cases as of Mar. 28th. And I also include Japan. (Because I am a Japanese...)
・I define the date of national "social distance" policy as the day when the government impose nationwide behavioral change towards keeping social distance such as school close, bars and restaurants close, sports events cancelled nationwide, and/or work at home.
・I define the # of confirmed death of that day as the number of accumulated number of confirmed deaths by the previous day when the national "social distance" policy becomes effective. (For example, school close policy is announced on Feb. 27th, and become effective on Mar. 2nd. # of confirmed deaths is the accumulated number of confirmed deaths by Mar. 1st.)
・These definitions might be somewhat different from that of Eisuke's report, the implication of the analysis is consistent with each other.
・I categorize the BCG vaccination policy into three, which are Mandatory, Past Mandatory and Only specific groups. "Mandatory" means the country takes current national BCG vaccination policy for all. "Past Mandatory" means the country took national BCG vaccination policy for all in the past. "Only specific groups" means the country recommends BCG vaccination only for specific groups or no recommendation at all.

[Data source]
▼Population(Million)
https://www.worldometers.info/world-population/population-by-country/
▼Total cases and total deaths as of Mar. 28th.
https://www.worldometers.info/coronavirus/
▼The starting date of national "social distance" policy in each country( Below is the sample of US, you can easily find the similar site by Wiki by changing the name of the country.)
https://en.wikipedia.org/wiki/2020_coronavirus_pandemic_in_the_United_States
▼# of confirmed deaths of that day
(For most countries other than Hubei and Japan)
https://www.worldometers.info/coronavirus/
(Only for Hubei and Japan whose chronological data cannot be taken from above)
https://github.com/CSSEGISandData/COVID-19/blob/master/archived_data/archived_time_series/time_series_19-covid-Deaths_archived_0325.csv
▼BCG vaccination policy and Year BCG vaccination stopped
http://www.bcgatlas.org/

[How to calculate other params]
▼Adjusted # of confirmed deaths of that day (per 100M population) (=X)
Accumulated # of confirmed deaths as of that day divided by the population and multiplied with 100M.
▼Adjusted # of confirmed deaths (per 100M population) as of Mar. 28th.(=Y)
Accumulated # of confirmed deaths as of  Mar. 28th. divided by the population and multiplied with 100M.
▼Days of doubling in # of total deaths after social distancing
This means days in which # of total deaths becomes double after social distancing. The larger it is, the slower the spread speed is.
It is calculated as # of days after national social distancing introduced, divided by Log2(Y/X) where X is "Adjusted # of confirmed deaths of that day (per 100M population)" and Y is "Adjusted # of confirmed deaths (per 100M population) as of Mar. 28th."

Here's the analysis and the findings.

Most remarkable finding is the correlation between the BCG vaccination policy and days of doubling in # of total deaths after social distancing.
・In the countries where BCG vaccination is mandatory, it takes 7-9 days for the # of deaths becomes double. China except for Hubei shows 11 days, much slower than other countries. In Portugal, the number is only 2 days to double, much faster than the other countries that take mandatory BCG policy.
・In the countries where BCG vaccination is past mandatory or only for specific groups, it only takes 2-4 days for the # of deaths becomes double.
・In some countries, # of deaths of the starting day of national social distancing policy is zero, we cannot calculate the days of doubling.

Thanks to the great work by my ex-colleagues(Eisuke-san and Jun-san), we can well recognize the current situation of coronavirus spreading in each country in terms of the two key factors of "the timing of introducing national social distancing policy" and "BCG vaccination policy".

We can categorize the countries by these two factors. Firstly, I divide these countries into two by whether # of confirmed deaths of that day is over 50 (Later social distancing) or not (Earlier social distancing) Secondly, I divide these countries into two further by the BCG vaccination policy. (Mandatory or Not)
Category1 (Later social distancing and NOT Mandatory BCG vaccination)
・・・Italy, Spain, France, UK, Switzerland
Category2(Earlier social distancing and NOT Mandatory BCG vaccination)
・・・USA, Germany, Netherlands, Austria, Belgium, Canada, Norway, Australia, Israel
Category3(Later social distancing and Mandatory BCG vaccination)
・・・Iran, Brazil(modified on 12th Apr.)
Category4(Earlier social distancing and Mandatory BCG vaccination)
・・・China(Hubei), China(w/o Hubei), South Korea, Portugal, Japan

Note: If we have the data of Wuhan in China, the # of confirmed deaths per capita might be larger than that of Hubei province as a whole. In that case, China(Wuhan) might be categorized into Category3.

As my ex-colleagues discussed in their report, BCG vaccination has proven to be safe and cost efficient while social distancing impose a heavy burden on people, society and business. Best mixture of these two countermeasures are to be well considered in each country. 

Further discussion and analysis might be as follows.
・Medical verification should be conducted before any actions based on this hypothesis are taken.
・I only pick up the top 20 countries in terms of # of confirmed cases, but we can analyze more countries in the same way shown above.
・I don't take the timing gap between countermeasures and their results into consideration. # of deaths is a lagging indicator which follows real impacts. To be more accurate, the doubling time should be calculated using the data after a certain period of time (2 to 3 weeks) from the date when the policy is implemented.
・I don't include the medical capacity in each country, which could impact on # of deaths in a rapid spreading situation.
・I don't take into account the difference of BCG stains by country as mentioned in Jun-san's report. If we take it into account, we might get further implication on the impact of the difference of the BCG stains.
・It might be important when the mandatory BCG vaccination policy was introduced. The later it is, the more elderly people who haven't taken it, which in turn leads to higher risks to become critical. 
・The situation in each country might depend not only on how early the national social distance policy is introduced but also on how strict it is. The further investigation can address this point.

Bunshiro Ochiai
I declare no conflicts of interest associated with this report.