As federal health officials offer more evidence that the mercury-containing vaccine preservative thimerosal is safe, many vaccine experts say in retrospect that the U.S. Food and Drug Administration's decision to remove it from childhood vaccines may have done more harm than good by raising public fears.

And still others argue that research and funds still being spent on exploring the risks of thimerosal could be directed to more productive enterprises.

A new study published in the New England Journal of Medicine concludes that early exposure to thimerosal does not cause any neurological problems. Thimerosal, used in vaccines since the 1930s, has been a topic of controversy since the FDA banned it in 1999.

Some claim that the additive causes autism and other brain development disorders in children. But the latest study joins a growing body of literature that shows thimerosal is safe and causes no long-term negative effects on children's health.

Although no concrete evidence at the time showed that thimerosal was harmful, the Centers for Disease Control and Prevention and the American Academy of Pediatrics pushed for its elimination to quell the fears of parents who might otherwise not get their children vaccinated.