TUESDAY, Dec. 9, 2003 (HealthDayNews) -- The preservatives, additives and various other substances added to childhood vaccines are safe.
That's the conclusion of a summary of existing studies that appears in the December issue of Pediatrics.
Besides the actual vaccine agent, vaccines often contain small amounts of proteins, antibiotics and other materials -- such as mercury, aluminum, formaldehyde, gelatin and yeast.
This array of substances has provoked some controversy about vaccine safety.
"Parents are quite confused," says Dr. Carol J. Baker, a member of the American Academy of Pediatrics' (AAP) committee on infectious diseases and a pediatric infectious disease specialist at Texas Children's Hospital in Houston. "I think there are more questions asked today than there were five or 10 years ago."
Many of those questions have had to do with thimerosal, a mercury-containing preservative. Although no scientific evidence has linked thimerosal with adverse effects, it was pulled from most childhood vaccines in 2001.
Thimerosal contains ethylmercury, which many people confuse with methylmercury, a metal found naturally in the environment.
The controversy over thimerosal's safety was always a theoretical one, says study author Dr. Paul A. Offit.
"There is no evidence at all that that was based on something that was real," says Offit, director of the Vaccine Education Center and chief of infectious diseases at the Children's Hospital of Philadelphia.
"Ethylmercury is not methylmercury and it has a half life. It is excreted much more quickly and is not taken up into the central nervous system," Offit says. Methylmercury, on the other hand, "is known to be more dangerous and is known to accumulate."
"Levels of mercury [in vaccines] are still well within what any reasonable person would consider to be safe -- meaning absolutely safe -- not just medically safe (the benefit outweighs the risk) but the legal definition of safe, truly free of harm," Offit adds.
"We live on the earth and the earth has heavy metals on it -- lead, mercury, aluminum -- so we'll always be exposed to trace quantities. The problem is that people don't distinguish those things. They think that any level is bad and that's just not true," he says.
The new study even suggests the removal of thimerosal from most vaccines has had some adverse consequences. In 1997, U.S. health officials advised hospitals to defer giving the hepatitis B vaccine to infants whose mother tested negative for the virus. Misunderstanding those recommendations, some hospitals did not give the vaccine to any newborns, including three infants whose mothers had the virus. A 3-month-old baby at one hospital who also did not receive the vaccine died of hepatitis-B induced liver failure, the study says.
"Because of this 'controversy,' which I think is largely a self-made controversy, the AAP asked that thimerosal be removed in an expeditious manner, saying 'there is no evidence to suggest levels are harmful but to make safe vaccines safer,' " Offit says. "If it's not harmful, how does it make it safer."
Aluminum salts, which are used in vaccines to enhance the immune response, are also safe, Offit concludes, as are levels of antibiotics and various other substances used in vaccines.
Possible rare problems may come from gelatin and egg proteins also found in vaccines. Children allergic to either gelatin or eggs may have severe reactions, which is why physicians need to pay particular attention to this issue, the study says.
Otherwise, the amounts of various metals and other compounds in vaccines are just too small to cause any concern, according to the study.
"If I chose to drink 10 gallons of water at one sitting, I could lower my serum sodium to the point that I had a seizure. I probably could do that," Offit says. "It doesn't mean that water is not safe. It just means I shouldn't drink 10 gallons at one sitting."
Barbara Loe Fisher is co-founder and president of the National Vaccine Information Center, which, according to its Web site, "supports the right of Americans to exercise informed consent and make educated, independent vaccination decisions for themselves and their children."
She's not ready to buy into Offit's conclusions.
"Certainly a review of the literature is one thing that is not anything that would be considered a definitive answer to the question of whether additives and preservatives are associated with adverse effects," Fisher says. "A review of the literature is not going to do much to answer questions until proper scientific investigation is done."