Part of the earlier 2003 SARS disease deaths were due to an over reaction by the human being’s immune system called a Cytokine Storm.

This may be happening in COVID-19 too
and would explain why babies get mild symptoms but +60 year olds die.

https://medicalxpress.com/news/2020-03-covid-host-disease.html

Sample quote

Q. Are there ways to measure CSS, and are those measurements being done?

A. An elevated serum ferritin test—which is cheap, readily available and quick—is a good first step for screening for CSS. There are a variety of other tests that can then help confirm or deny the presence of a cytokine storm syndrome.
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