The injectable, multi-dose H1N1 vaccine contains the mercury-based preservative thimerosol to reduce risks of bacterial contamination. The presence of thimerosol has once again raised concerns whether there are risks posed to children when the tiny amount of mercury contained in thimerosol is included in a vaccine. In a recent issue of the Journal of Pediatrics, however, a team of scientists supported by the National Institutes of Health reported findings that should alleviate those concerns. The researchers, led by author Michael E. Pichichero, MD, Director of the Rochester General Research Institute, Rochester General Hospital, Rochester, NY evaluated levels of mercury in the blood of the smallest children -- prematurely born and low birth weight infants after they received a dose of a childhood vaccine containing thimerosol. They found the levels of mercury were exceedingly low.

The issue of administering vaccines containing mercury has been controversial because at very high levels mercury is known to cause organ damage (brain/kidneys). Consequently in 2001, as a precaution, at the prompting of the American Academy of Pediatrics, the Centers for Disease Control, and the Food and Drug Administration, the use of thimerosol in childhood vaccines was reduced or eliminated. However, after examining the evidence the Institute of Medicine issued an opinion that an association between thimerosol exposure and autism was not supported by the evidence. Nevertheless the contention that mercury in vaccines causes autism continues to be debated. The newly released multi-dose, injectable H1N1 Influenza vaccines contain the preservative thimerosol and thimerosol is 50% ethyl mercury, which has sparked a renewed debate on the safety of administering this new influenza vaccine.

The purpose of the study was to find out how much mercury from a vaccine containing thimerosol stays in a child's body," said Dr. Pichichero. "What we found was that blood mercury levels before vaccination were often detectable, even at a level similar to many children after the vaccination. By just breathing the air, mothers were passing to their unborn infants some slight amounts of mercury. The mothers did not eat fish that contains mercury, so in the United States and other countries where fish is consumed by pregnant women the levels of mercury would be presumably even higher. After the babies were given vaccines containing thimerosol, their blood levels of mercury did rise to very low levels and then fell rapidly to baseline levels by day ten after the vaccination."

Since thimerosol has been largely removed from vaccines in the US since 2001, this study of 72 newborn infants was conducted at the Hospital Durand in Buenos Aires, Argentina. In Argentina, like many countries of the world, vaccines are purchased through sources supported by the World Health Organization and the WHO has rejected the notion that thimerosol in vaccines is unsafe. This is the third and final study by Dr. Pichichero and his colleagues that tested mercury levels following the injection of vaccines containing thimerosol. Previous studies were conducted on term newborns, and on 2-and 6-month old infants. In those studies, the researchers also found the mercury levels in the vaccinated children were very low and quickly returned to pre-vaccine levels, usually within three to seven days. In 1999, when the first concerns about thimerosol in vaccines was raised, it was presumed that the ethyl mercury in thimerosol would behave in the same manner as methyl mercury in fish after ingested. The three NIH-supported studies clearly refuted that idea.

Dr. Pichichero and colleagues concluded that with this latest data, it is time to recognize that the risk of exposure to thimerosol in vaccines is minimal to non-existent. "The H1N1 vaccine is safe and should be given to those at risk as recommended by the US Centers for Disease Control," Dr. Pichichero said.

Rochester General Research Institute is part of the Rochester General Health System (RGHS) in Rochester, NY. The Research Institute is focused on clinical and translational research in the areas of infectious diseases and immunology, cardiovascular diseases, cancer, and innovations in

biotechnology. The Rochester General Research Institute has alliances with the Rochester Institute of Technology, the Cleveland Clinic and Roswell Park Cancer Institute.