When the New England Journal of Medicine reported last month on the 2005 measles outbreak, it did us all a favor. A 17-year-old Indiana female, who hadn’t been vaccinated, brought the virus back from Romania, then attended a church gathering of 500 people, leading to 34 confirmed cases (32 of which had not been vaccinated).

Measles is preventable: 99% of those who receive the two-step vaccination develop immunity. The measles vaccine uses a live attenuated virus, which means a deactivated virus that can still provoke immunity but no longer get people sick.

However, there’s a growing irrational fear of vaccinations that is not connected to fact. This fear leads to disuse of a crucial preventative. Thimerosal,which in one study caused laboratory mice to be irritable and tremorous, has never been shown to cause serious problems in children. But the fear of its being the culprit for the increasing rate of autism has given rise to a fear of vaccines in general.

This fear  has extended from traditional MMR vaccines to the newly released MMR-varicella (chicken pox) vaccines, Priorix-Tetra (GlaxoSmithKline), and ProQuad (Merck). Fear of autism has also been linked to MMR vaccines, despite the fact that they don’t contain thimerosal. A study in Pediatrics in July 2006 cleared both MMR and thimerosal-containing vaccines as NOT being linked to autism, but the fear remains.

While it’s understandable that parents are concerned about vaccines their child receives, the measles vaccine requires 100% compliance to effectively prevent reoccurrence and control spread of a deadly disease. In 2005, 98% of the people who lived in the area where the measles outbreak occurred had been previously immunized, a crucial factor in containing the outbreak.

Nervous fear of a lifesaving vaccine must be outweighed by a much more healthy fear of a killer disease.

Marc Siegel, MD, is an internist and associate professor of medicine at New York University and the author of False Alarm: The Truth About the Epidemic of Fear