Investigations

Study: Mercury in Vaccines at Safe Levels

Pediatrician Michael Pichichero and colleagues at the Medical Center are hoping to deliver a small dose of reassurance in the debate over the safety of infant and toddler vaccinations.

In the first detailed analysis of blood mercury levels in infants who received vaccines containing the preservative thimerosal, the team found that mercury levels in vaccinated children in the United States fall comfortably below current safety limits. The results, published last fall in the journal The Lancet, also found that infants flushed the form of mercury contained in vaccines from their system in six to seven days—six times faster than expected.

Pichichero, lead investigator of the study and professor of microbiology and immunology, pediatrics, and medicine, has launched a larger, international study to elaborate on last fall’s results.

“Every day we see families who are reluctant to have their children vaccinated because of this issue,” says Pichichero. “We work with them, and many decide to go ahead with vaccinations, but some do not, and so they put their children at increased risk for developing serious diseases.

It’s no longer a routine office visit.”

The issue is at the core of a national debate over the safety of vaccines. While some parents and politicians have asserted that the minuscule amounts of mercury used in vaccines could be responsible for a range of disorders including autism in some children, Pichichero’s study adds evidence to the argument by most pediatricians and public health officials that vaccines are safe.

Thimerosal critics point out that the rise in the number of autistic children coincides with the period the preservative was used in vaccines—from the 1930s to the 1990s. Signs of autism in children begin to appear between the ages of 1 and 2 years old, shortly after the age when children are vaccinated against several childhood diseases.

In 1999, under pressure from the American Academy of Pediatrics and public health officials, manufacturers removed thimerosal from vaccines used in the United States. The preservative is still widely used in other countries to make vaccines available to millions of children at a lower cost.

In response to the debate, Rochester researchers were asked by the National Institute of Allergy and Infectious Diseases to conduct a study of 61 infants, 40 of whom received thimerosal-containing vaccinations for diphtheria, tetanus, whooping cough, and hepatitis B, while the rest received the same vaccines without the preservative. Most of the children had mercury blood levels of 1 or 2 nanograms per milliliter, and only one had a level as high as 4.11 nanograms per milliliter. The Environmental Protection Agency’s most stringent safety limit for mercury blood level is 5.8 nanograms per milliliter.

“The results are very reassuring,” Pichichero says. “The amount of mercury is well below all established safety levels.”

In January, Pichichero and colleagues began a second study of 200 children in Buenos Aires, Argentina, where vaccines with thimerosal are still used. While no longer used in the United States as a preservative in vaccines, thimerosal helps keep down the costs of vaccines in poorer countries because thimerosal-containing vaccines can be stored in fewer, large multidose vials, which are less expensive to produce.

Pichichero says it’s a “critical issue of life and death” for poorer countries that may not be able to afford the more expensive single vials.

“In countries that are still confronting diseases like whooping cough and tetanus and measles, where millions of children die of the disease, there is no argument,” Pichichero says. “Where people are dying of these diseases, switching to a thimerosal-free vaccine would raise the prices such that millions of children would go unvaccinated.

“For them, it’s a critical issue of life and death.”