High-quality analysis of the former East/West Germany testing the BCG hypothesis... if the herd(external) immunity effect is added...

I like reading negative papers about the BCG hypothesis since they give me another angle to think critically about the BCG hypothesis.

Here comes a report analyzing the former East/West Germany testing the BCG hypothesis. Interestingly, this report comes from the Federal Reserve Bank of New York!


The Spread of COVID-19 and the BCG Vaccine: A Natural Experiment in Reunified Germany
Number 926
May 2020
Authors: Richard Bluhm and Maxim L. Pinkovskiy

This is a report and not a paper peer-reviewed, but this report is much higher quality than the peer-reviewed paper from Israel. Probably, the authors are econometrics researchers and their analytical skills are much better than Dr. Ferguson or Dr. Nishiura.

Don't the authors know the herd(external) immunity effect?

This report clearly analyzes the big difference between the former East/West Germany. It is fantastic since it looks at the distance from the old border. The difference is not linear but a sharp drop between the old border.

And they look at the two age groups; 15 to 34 and 35 to 59. Most of the former age group were not BCG vaccinated in ex-East or ex-West. Most of the latter age group were BCG vaccinated in ex-East while about half of the latter age group were BCG vaccinated in ex-West.

The analysis shows there are big differences in both age groups as below.

This report concludes that as there remains a difference in the age group of 15 to 34 who had not BCG vaccinated, the difference should be attributed to the factors other than BCG vaccine. Wait for a second! Don't the authors know the concept of herd immunity?? If the people around you are immune to the disease, you are protected even if you are not immune to the disease.

You can understand how big the herd(external) immunity effect is by reading the following post. Portuguese senior people over 80 years old who didn't have BCG vaccinated are protected by the younger generation who had BCG vaccinated.


Also, I wonder why this report does not dig into the death numbers.

The two important population factors for the west of Germany

This report covers major confounding factors but let me add two important population factors.

  1. When reunification happens, 12% of ex-East Germany population moved to the West, especially young female.
  2. Germany has the highest percentage of immigrants, 11% of the total population and I guess they live in the West part mostly and had BCG vaccination in their home countries.
These two factors can be a reason that ex-West Germany has a lower COVID-19 death rate than the other West Europe countries which abandon the BCG vaccination while the death rate of ex-East Germany is on the same level of the other East Europe countries.

Can the commute factor be "the other factor"?

This report picks up and attributes "the other factor" to the commute factor as people rarely commute crossing the old border. The virus spread in the west earlier. And the last sentence of its conclusion is;
It is not unimaginable that the raw discontinuity we documented will eventually disappear or even turn around if the infection spreads to a poorer, older and more disease-prone population in the East. 
This report is based on 26 April data.

We started to look at the Germany data on 27 March, analyzed several times and the most updated analysis is below on 20 May. The difference constantly remains from 27 March to 20 May for three months though ex-East is a more aging society. I am sure that the doubling time is different for ex-West and ex-East and the timing is not the reason. I predict that the last sentence of this report will be proven wrong in a month or so.

Let's add the BCG strain factor

The BCG vaccination policy has been very complex. This report summarizes it as Table 1.

This is a helpful summary but it misses an important factor; the BCG vaccine strain. We found that ex-West had used BCG Denmark strain while ex-East had used BCG S4-Jena. We cannot find good information about BCG S4-Jena but BCG S4-Jena seems to be a stronger strain than BCG Denmark.


  1. This comment has been removed by the author.

  2. Hi Jun, great analysis.
    BCG S4-Jena is a derivative of a Swedish BCG substrain that was imported directly from the Paris Pasteur Institute in the 1920s -

    Please see this diagram, according to it, Swedish is grouped together with Tokyo and Russia strains, so it make sense that S4-Jena is also stronger - https://www.researchgate.net/figure/The-genealogy-of-BCG-strains-based-on-Keller-et-al-15-displays-a-series-of-genomic_fig3_256102624

    Kind regards,

    1. Hi Rado,

      The BCG Sweden is the generation in-between Russia/Japan and Denmark/Glaxo.

      The chart below helps us to understand the BCG strains.

      And from these two papers, I think the BCG Sweden strain has some different characteristics from the BCG Japan/Russia strain.


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