References

Various articles related to COVID19 and SARS-CoV-2.

Comparison of the clinical characteristics and mortality of adults infected with human coronaviruses 229E and OC43
229E was found to have a fatality rate, in those with severe enough disease to be hospitalized, of 25%. Yet, most of us are first exposed sometime in our youth, and therefore have a cold from it.

Why COVID-19 Is Here to Stay, and Why You Shouldn’t Worry About It
Rich article, well worth reading, lots of links, mentions the above 229E which has had many variants.

Sunlight and Vitamin D
Summary of everything on this topic.

49 minutes exposure needed daily when sun is 45° above horizon at noon.
Webb 2011 DOI: 10.1111/j.1751-1097.2011.00898.x

Natural immunity vs vaccination

Necessity of COVID-19 vaccination in previously infected individuals
Not one of the 1359 previously infected subjects who remained unvaccinated had a SARS-CoV-2 infection over the duration of the study.