The best form of prevention against human infection through bacteria, viruses and other parasites is ozone disinfection of wastewater and drinking water as a highly effective, well-known method. As a therapeutic measure, various preclinical studies showed promising results, which are being revisited and reconsidered in times of pandemics and led to interesting results in recent clinical trials and reports, as presented by the example of protective measures against covid-19 in particularly vulnerable clinical personnel. In patients with rheumatoid arthritis, repeated ozone treatments have led to new findings in the "immunomodulation" through ozone. The more effective immune response is discussed as the response of innate immune memory and opens interesting aspects for complementary treatment of autoimmune diseases.