Why is there a high discrepancy in mortality rates for COVID-19 in western Europe?

Examining the mortality rates of different countries in Western Europe, one can not be but shocked at the high mortality rates recorded by some of the most developed countries in the world; UK (14%), France (15%), Italy (14%), Netherlands(13%), Belgium (16%), Spain (9.5%) (The cumulative number of deaths in these countries constitute about 40% of the total deaths worldwide). But what is more surprising, why have these countries recorded these high mortality rates while other neighboring western European countries have recorded a much lower mortality rate? e.g. Germany (4.5%), Portugal (4.3%), Switzerland (6%), Austria (4%), and Ireland (7%). Is it because of the superiority (or at least the better preparedness for emergencies) of the health system in these countries to those of the former group? Or is it due to a different strain of COVID-19 infecting different countries? Or is due to the different responses (and timing) of the governments of these countries to the pandemic? Any ideas, thoughts or theories on this issue. Any references is appreciated.

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