No matter how many times the medical community reassures parents that vaccines are safe and necessary to prevent life-threatening diseases, some people remain unconvinced.
"I believe that herd immunity is a complete myth," says J.B. Handley, co-founder of an autism advocacy organization called Generation Rescue that is critical of the way vaccinations are carried out in the U.S. "It's a tactic used to scare the public."
Handley, a father of three in Portland, Ore., has an 8-year-old son with autism. He believes that the cocktail of immunizations his son received when he was 13 months old is to blame
"Do I think a vaccine appointment was a trigger for his decline into autism? Yeah, with every fiber of my being I do," he says. "And I've met several thousand parents who feel exactly the same way."
Handley insists that his organization, led by actress-turned-activist Jenny McCarthy, isn't opposed to vaccines altogether but believes they shouldn't be given until children turn 2 years old and their immune systems are mature enough to handle them.
"We think too many shots are given to children too early in their life and administered in too unsafe a manner, meaning simultaneously," he says.
Handley points to a 2010 study in the Polish journal Acta Neurobiologiae Experimentalis in which researchers administered a series of vaccines to infant rhesus monkeys. The timing of the shots was designed to mimic the childhood immunization schedule used in the U.S. from 1994 to 1999. The brains of the immunized monkeys appeared to be less mature than the brains of the other animals, the researchers reported.
But researchers have affirmed the safety of the U.S. vaccine schedule in numerous studies, including a 2002 review article in the journal Pediatrics, a 2010 study in Pediatrics and in many clinical trials in children, says Dr. Paul Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia.
"Why would you delay vaccines?" Offit says. "You have diseases like pneumococcus, whooping cough, Hib and chickenpox which can severely, and fatally, infect young children. Why would you ever take the chance?"
The science on the safety of the current vaccination schedule vaccines is "exhaustive," agrees Dr. Julie Boom, director of infant and childhood immunization for the Center for Vaccine Awareness and Research at Texas Children's Hospital in Houston.
Experts acknowledge that there have been rare instances of children who had poor reactions to vaccines. The whole-cell diphtheria-tetanus-pertussis vaccine that was developed in the 1940s was phased out in the U.S. in the late 1990s because studies suggested it could have contributed to neurological problems including seizures, lasting brain damage or death in about 1 out of every 140,000 doses. In a few extraordinary cases, children with compromised immune system or other health problems may have adverse reactions to vaccines.
"The problem is that people lose perspective about the risks and benefits," Boom says. "The risk of getting pertussis or whooping cough without vaccination is higher — a lot higher — than the one-in-a-million chance of having an untoward effect from a vaccine."
The link between autism and vaccines — famously put forth in a 1998 article by Dr. Andrew Wakefield in the British medical journal Lancet that was later found to be fraudulent — has been debunked by a variety of medical studies. Yet Offit says he can understand why some parents remain suspicious.
"They see their children get pinned down to that crinkly white paper and get five shots at one time, against their will, while they're crying," he says. Under such circumstances, it's easy to persuade parents "that this is something to fear."
But the tide may be turning. Last year, Lancet retracted Wakefield's autism-vaccine study, and vaccine resistance is beginning to wane, some doctors say.
"There's certainly not a day that goes by that I don't have a significant conversation with at least one family regarding their concerns about vaccines," says Denver pediatrician Noah Makovsky, but "it is definitely on the decline compared to where it was a year ago."
Nowadays, he says, "It's a much shorter conversation."