A memo from the drug giant Merck & Co. shows that nearly a decade before the first public disclosure, senior company executives were concerned that infants were getting an elevated dose of mercury in vaccinations containing a widely used sterilizing agent.
The March 1991 memo, obtained by the Times, said that 6-month-old children who received their shots on schedule would get a mercury dose up to 87 times higher than health guidelines for the maximum daily consumption of mercury from fish.
"When viewed in this way, the mercury load appears rather large," said the memo from Dr. Maurice R. Hilleman, an internationally renowned vaccinologist. It was written to the president of Merck's vaccine division.
The memo was prepared as U.S. health authorities were aggressively expanding their recommended immunization schedule by adding five new shots for children in their first six months. Many of the shots, as well as some previously included on the vaccine schedule, contained thimerosal, an anti-bacterial compound that is nearly 50 percent ethyl mercury, a neurotoxin.
U.S. health officials disclosed for the first time in 1999 that many infants were being exposed to mercury above health guidelines through routine vaccinations. The announcement followed a review by the Food and Drug Administration that was described at the time as a first effort to assess the cumulative mercury dose.
But the Merck memo shows that at least one major manufacturer knew of the concern much earlier.
Merck officials would not discuss the contents of the memo, citing pending litigation.
Separately, the company is trying to fend off a legal onslaught over Vioxx, the popular painkiller it introduced in 1999. Merck, based in Whitehouse Station, N.J., faces hundreds of lawsuits claiming that the drug caused heart problems and that the company concealed the risks. Merck, which in September pulled Vioxx off the market, has denied the allegations.
The legacy of thimerosal, meanwhile, is causing problems for Merck and other companies.
More than 4,200 claims have been filed in a special federal tribunal, the Vaccine Injury Compensation Program, by parents asserting that their children suffered autism or other neurodevelopmental disorders from mercury in vaccines. A handful of similar claims are awaiting trial in civil courts.
Thimerosal has been largely removed from pediatric vaccines in recent years in what health officials have described as a precautionary measure.
Merck and other vaccine makers, along with many government health officials and scientists, say there is no credible evidence of harm from the amounts of mercury once widely present in children's shots.
The seven-page Merck memo was provided to the Times by James A. Moody, a Washington lawyer who works with parent groups on vaccine safety issues. He said he obtained it from a whistle-blower whom he would not name.
The memo provides the "first hard evidence that the companies knew - or at least Merck knew - that the children were getting significantly more mercury" than the generally accepted dose, Moody said.
Hilleman, a former senior vice president of Merck, developed numerous vaccines for the company. Hilleman, 85, now director of the Merck Institute for Vaccinology, had officially retired and was a consultant to Merck when he wrote the 1991 memo. He declined to be interviewed.
The Los Angeles Times is a Tribune Publishing newspaper.