Merck & Co. continued to supply infant vaccine containing a mercury preservative for two years after declaring that it had eliminated the chemical. Thimerosal, which is nearly 50 percent ethyl mercury, has largely been eliminated from most routine childhood vaccines, although it is present in most flu shots. More than 4,200 parents have filed claims in the federal Vaccine Injury Compensation Program, alleging that their children suffered autism or other neurological disorders from mercury in their shots.