In the United States an estimated 225,000 deaths per year have iatrogenic causes, with only heart disease and cancer causing more deaths.

Human H1N1 virus reappeared in 1977, in the Soviet Union and China. Virologists, using serologic and early genetic tests, soon began to suggest the cause of the reappearance was a laboratory escape of a 1949-50 virus, and as genomic techniques advanced, it became clear that this was true. By 2010, researchers published it as fact.