  An important parameter for COVID-19 is the case fatality rate (CFR). It has
been applied to wide applications, including the measure of the severity of the
infection, the estimation of the number of infected cases, risk assessment etc.
However, there remains a lack of understanding on several aspects of CFR,
including population factors that are important to CFR, the apparent
discrepancy of CFRs in different countries, and how the age effect comes into
play. We analyze the CFRs at two different time snapshots, July 6 and Dec 28,
2020, with one during the first wave and the other a second wave of the
COVID-19 pandemic. We consider two important population covariates, age and GDP
as a proxy for the quality and abundance of public health. Extensive
exploratory data analysis leads to some interesting findings. First, there is a
clear exponential age effect among different age groups, and, more importantly,
the exponential index is almost invariant across countries and time in the
pandemic. Second, the roles played by the age and GDP are a little surprising:
during the first wave, age is a more significant factor than GDP, while their
roles have switched during the second wave of the pandemic, which may be
partially explained by the delay in time for the quality and abundance of
public health and medical research to factor in.
