13% of Americans have not been infected with Covid-19.  Roughly the same number is true in other developed countries where epidemiologic studies have been done.  Is it simply good luck or is some other force at work?   

As it turns out a recent bit of research published in the journal Nature points toward genetics.  Scientists in the UK placed infecting doses of Corona virus in the nostrils of study volunteers.  The small minority who did not become ill had high levels of gene HLA-DQAZ a gene that controls the production of interferon (an immune protein that does what the name implies:  interferes with viral replication).  The study participants who became ill produced modest amounts of interferon, but not enough to stop the virus from reaching the critical mass necessary to cause infection.