As it turns out, and this retro study is not alone in confirming it; antihistamines in general have unique antiviral properties that seem to prevent the silent hypoxia from progressing to death.

In this case a small group of nursing homes avoided any deaths related to covid, even though some of their residents required corticosteroids and oxygen.

Other studies have confirmed that in-vitro, common antihistamines like benadryl or hydroxyzine have been able to prevent the hypoxia caused by the pneumonia-inducing nature of the virus (which attacks the lungs without congestion, leading to oxygen levels plummeting out of nowhere).

What is unique, is that it seems effective for those in high risk groups, such as elderly patients.

The science behind it is incredible, and not perfectly understood yet, but scientists studying the effect hypothesize that it is because of H-1 and H-2 histamine receptors found in the lungs as well, and that it may be caused by the antihistamines binding to the the ACE2 pathway used by the virus itself, preventing it from completing its replication cycle.

[link to www.ncbi.nlm.nih.gov (secure)]