In recent years, measles outbreaks in Pennsylvania and California sickened some 500 mostly unvaccinated men, women, and children—reminders that once-common childhood infectious diseases still threaten us. Some parents believe, however, that routine childhood vaccines are fraught with serious risks that outweigh their benefits. News & Views interviewed three leading pediatricians at NYU Langone Medical Center, each with expertise in vaccines, to help sort out the facts from the fallacies.

Vaccines cause autism.

FALSE. “Hundreds of studies have looked at this issue and not a single one has found a link between vaccines and autism,” notes pediatrician Benard Dreyer, MD, who also serves as president of the American Academy of Pediatrics. The one study that raised this possibility was found to have been based on falsified data and has since been retracted. Adding to the confusion, symptoms of autism tend to arise around the same time children get several of their vaccines. “But just because these two events occur simultaneously doesn’t mean there’s a correlation, and the science shows there isn’t,” says William Borkowsky, MD, director of the Division of Pediatric Infectious Diseases.

It’s ok to change a child’s immunization schedule to avoid overwhelming his or her immune system with too many vaccines.

FALSE. Multiple vaccines do not overwhelm a child’s developing immune system, notes Dr. Borkowsky. The timing of each vaccine is based on when the immune system will generate the best response, which is balanced with the need to provide protection at the earliest possible age. Altering that carefully designed schedule—or the vaccine dosage—could compromise a child’s ability to fight off disease, though exceptions may be made.

Vaccine additives are dangerous.

FALSE. A variety of ingredients are used to stabilize vaccines or enhance their effectiveness, and studies show that none of these additives poses any health risks. “All vaccines go through years of rigorous safety testing before they are brought to market,” explains pediatrician Arthur Fierman, MD, director of the Division of General Pediatrics.

Since most childhood diseases are now rare, vaccines are no longer necessary.

FALSE. Thanks to vaccines, diseases like mumps and whooping cough have largely disappeared. But the viruses and bacteria that cause them have not. “The only infectious agent that we’ve ever exterminated is smallpox,” notes Dr. Borkowsky. “If we don’t continue to vaccinate children, the other diseases will return—in epidemic proportions.”

If most children get vaccinated, the ones who are not immunized will be protected.

TRUE. This phenomenon is known as herd immunity. “But once vaccination rates dip below 80% for healthy people and 90% for high-risk people, herd immunity no longer works,” explains Dr. Borkowsky. The appearance of just one case in an under-vaccinated community can cause that disease to spread. The experts note that vaccines are not 100% effective and having a communicable disease in childhood does not necessarily confer life-long immunity.

Some vaccines are dangerous for children whose immune systems are compromised.

TRUE. A few vaccines may pose harm to children with severe immune disorders. But there’s no blanket recommendation for whether immunocompromised children should or shouldn’t be vaccinated. “In the case of immune disorders, the safety and efficacy of vaccinations depends on the nature of the disorder, as well as the vaccine in question,” explains Dr. Fierman. “Parents who have any concerns should consult their pediatrician,” he says. “Learn as much as possible, but use your pediatrician as an interpreter.”