Historically, there has always been a degree of concern related to vaccination. While public health policy in the early 1900s was more concerned with the contamination of vaccine vials with microbes, such as tetanus, that could cause serious illness and potentially death, current vaccination concerns are centered on the apprehension of chemicals ‘contaminating’ vaccines. The modern day vaccination controversy regarding chemical contamination began as a result of environmental concerns regarding industrial by-products and heavy metals and intersected with the history of autism prevalence. It is important to understand the historical shift of contamination sources in understanding how the controversy regarding thimerosal came into contention.