Temperature threshold: Cold temperature
Different vulnerability situation was observed for moderate cold countries and extreme cold countries.
Moderate cold: The first ten countries (and number of death counts till 3rd April) in descending order are mentioned: Italy (13,917), Spain (10003), United States (6,053), France (4,503), China (3,326), Iran (3,160), United Kingdom (2,921), Netherlands (1,339), Belgium (1011) and Germany (872)2. These countries showing maximum vulnerability, belonged to the moderate cold category. Mean temperature varied between the range of around 275°K (2°C) to 290°K (17°C) .
Severe cold: Though Laboratory experiments to our knowledge did not conduct any study relating to lower temperature threshold, but Fig. 1 and 2a suggested, lower temperature threshold may also be important. Here are some statistics2 for reported case (and death) for countries below 275° K (2° C), e.g., Iceland 1319(4), Finland 1518(19) and Canada 11268 (138); all those showed comparatively low death count till 3rd April.