Margaret Dunkle's op-ed ("We don't know enough about childhood vaccines," July 11) is a dangerously misguided attempt to scare people away from vaccinating their children. Despite the fact that science has debunked Ms. Dunkle's claims, I am deeply concerned that presenting her views in The Sun will give them credibility they do not deserve and will lead parents to withhold vaccines from their children.

The consequences may cause serious harm to the public. Ten children died in an outbreak of whooping cough in California last year, and outbreaks of measles and meningitis have occurred elsewhere, including Maryland. Each of these outbreaks occurred in unvaccinated children. The anti-vaccine movement in this country is threatening to take us back to an era in which children frequently died from infections that can be almost completely prevented by vaccines.

Ms. Dunkle's main claim is that the current vaccine schedule gives children too many vaccines too early in life, and that this is somehow harmful to children. Quite the opposite is true. A thorough scientific review of this question in 2002, appearing in the journal Pediatrics, concluded that not only are multiple vaccines safe, but that they actually "prevent the weakening of the immune system." Hundreds of other scientific studies have demonstrated both the safety and effectiveness of vaccines.

Ms. Dunkle cites a recent study to support her claims, but she neglects to mention that the study was written by an economist, not a scientist, and that the very same economist is a well-known anti-vaccine activist. That same study has already been widely discredited by scientists who have pointed out its flawed statistical methods and cherry-picking of data.

Ms. Dunkle would like readers to think that this study will "rekindle the debate about vaccine safety," particularly aboutautism and vaccines. On that question, researchers have already conducted multiple studies, involving hundreds of thousands of children, and the evidence is overwhelmingly clear that vaccines do not cause autism.

Vaccines save lives. According to the CDC, if we could vaccinate every child born in the U.S. this year, we would save 33,000 lives, prevent 14 million infections, and save over $10 billion in health care costs. If Ms. Dunkle and other anti-vaccine activists succeed, children will fall ill, and some will die. Very young infants, the elderly, and people with compromised immunity are particularly at risk. We mustn't let Ms. Dunkle's fear-mongering and misinformation spread further.

Steven L. Salzberg, Baltimore

The writer is a professor of medicine and biostatistics at the Johns Hopkins University School of Medicine.