Schools play a key role in ensuring that children are being immunized against diseases, but conflicting research is making enforcement difficult.
When whooping cough first turned up in Westchester County, N.Y., a year ago, it wasn’t necessarily noteworthy. True, the contagious bacterial infection was once a major cause of death among infants and young children in the United States. But that was before widespread immunization, and Westchester County typically sees only five or six cases a year.
The 2003-04 school year was different for the wealthy New York City suburb. In October, local newspapers were reporting confirmed cases of whooping cough in two adults and 17 children in Westchester communities. By April, five infants had been hospitalized, and the outbreak had spread to nearly 100 people in the county, many of them children who were classmates.
|See the accompanying chart, "Immunization Schedule."||
The Westchester County health commissioner, Dr. Joshua Lipsman, is still counting cases. Most troubling, he says, is that "this outbreak began with unvaccinated children who were old enough to be vaccinated." Each year in the United States, 2.1 million children ages 19 months to 35 months are classified as "undervaccinated," lacking shots for infectious diseases such as whooping cough, hepatitis, and polio. Typically, studies show, such youngsters are members of racial or ethnic minorities living in poverty in urban areas with mothers who lack college degrees.
But the growing number of children who receive no vaccines at all fit a different profile, says Philip J. Smith, a mathematical statistician with the federal Centers for Disease Control and Prevention’s National Immunization Program.
Recent research puts the number of unvaccinated youngsters in the United States at roughly 17,000 a year, or 0.3 percent of children 19 to 35 months old. Those preschoolers tend to be white and male, to have married mothers with college degrees, and to live in households with annual incomes over $75,000, according to research led by Smith and published this month in Pediatrics, the scientific journal of the American Academy of Pediatrics.
That study of nearly 152,000 children also shows that the unvaccinated tend to be children of parents who are worried about potentially harmful side effects of immunizations, and who say that their doctors have no sway over their decisions to forgo vaccines for their children.
Perhaps most troubling of all from a public-health perspective are recent data showing that families with unvaccinated children tend to cluster in communities in certain parts of the country.
Westchester County, for example, was No. 6 on the list of counties with the highest numbers of unvaccinated children in the country, according to Smith’s analysis of national immunization data from 1995 to 2001. Los Angeles topped the list with 465 unvaccinated children.
"What we’ve seen around the United States is that unvaccinated children are very frequently at the bottom of outbreaks of vaccine-preventable disease," Smith says. "With no vaccines, these children are at risk for contracting pertussis, measles, and many other preventable disease, and they can then spread these diseases to other groups of children."
Driving the growing trend of vaccine avoidance is a seemingly endless supply of conflicting information and research about immunization safety.
A combination vaccine is more than one vaccine contained in a single shot. Many doctors and parents prefer that method because it allows a child to get several vaccines at once with fewer injections. Several combination vaccines are already in use, such as MMR (Measles, Mumps, Rubella), DTaP (Diphtheria, Tetanus, Pertussis), and Hib/Hepatitis B (Haemophilus Influenzae Type B/Hepatitis B).
SOURCE: Centers for Disease Control and Prevention
Immunizations have reduced the incidence of disease by more than 95 percent for every pediatric vaccine recommended for routine use before 1990, according to the CDC.
As the number of immunizations for children has increased, however, so have reports of vaccine side effects. That situation—combined with the scant experience younger generations have with the diseases controlled by vaccines—has led to an intense focus on the safety of vaccines, health experts say.
"For older generations, who saw children die from these diseases before there were vaccines, vaccination is a given," says Deborah A. Gust, a behavioral scientist with the CDC’s National Immunization Program. "But younger parents have had no experience with these diseases. What they’re mostly hearing about is side effects from the vaccines—and they have questions."
In an effort to answer those questions, the CDC and the National Institute of Health’s Institute of Medicine sponsored a panel of 14 independent experts in the areas of medicine, public health, and scientific research to study ongoing and emerging vaccine-safety issues. The committee first met in January 2001 and, for the next three years, explored some of the most controversial claims dogging this country’s immunization program.
Do the influenza and hepatitis-B vaccines lead to neurological disorders? Do multiple immunizations cause the immune system to malfunction? Are some vaccines at the root of sudden infant death syndrome? And do vaccines—particularly the shot for measles, mumps, and rubella, or MMR—trigger autism?
In a series of eight reports, the panel did recommend some areas that needed further research. But in no case did it find enough evidence of risk to recommend changing the nation’s current vaccine policies.
As for the MMR-autism debate, "that’s an easy one for me," says Dr. Marie C. McCormick, the committee’s chairwoman and a professor of maternal and child medicine at Harvard University. "The question has been out there for almost four years now, and 14 epidemiological studies have found no evidence of a causal relationship."
Though some advocacy groups and scientists disagree with that and other findings reached by the committee, the panel’s work leads to the conclusion that not having a child vaccinated is more dangerous than submitting him or her to the recommended regimen of shots.
Parents who opt out of immunization for safety reasons are "responding to a hypothetical risk, compared to the very real risk of some very bad diseases," McCormick says.
But conflicting evidence continues to emerge.
Barely a month after the Institute of Medicine panel released its report concluding that "the evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism," a new study of mice that suggests otherwise was released by Columbia University.
The central finding of the research—that the mercury preservative thimerosal can cause autism-like behavior in mice with a specific genetic susceptibility—made headlines and reinvigorated the arguments of parent activists.
Despite the controversy, many people appear to accept the health community’s assurances that vaccines are safe and beneficial.
By and large, the credit for ensuring that most children receive the recommended vaccines before they enter school goes to the states. No federal law requires that children be vaccinated, but all 50 states mandate that children be immunized against a range of infectious diseases such as measles, hepatitis B, pertussis, and tetanus before they enter school.
Experts say the laws are not airtight, though.
To begin with, all states permit medical exemptions from vaccination for people with immune-system problems, allergies to vaccine ingredients, moderate or severe illness, or other health problems, according to a paper written by Daniel A. Salmon, an associate director of the Vaccine Safety Institute at Johns Hopkins University in Baltimore.
In addition, 48 states allow children to opt out of compulsory vaccination for religious reasons, and 19 allow philosophical or personal exemptions in an effort to accommodate a minority that researchers say represents less than 1 percent of the population.
The CDC’s Smith writes in his study of unvaccinated children that "in many states, it is easier to claim a religious or philosophical exemption than to adhere to mandated immunization requirements."
In some cases, it’s as simple as checking a box when a child enters school, Smith says. And his study notes that states that allow philosophical exemptions to their immunization laws have had significantly higher estimated rates of unvaccinated children than states that do not allow exemptions.
There are consequences for states allowing exemptions, according to researchers.
What if a Child Misses a Shot?
For most vaccines, it is never too late to catch up on missed shots. Children who missed their first shots at 2 months of age can start later. Children who have gotten some of their shots but then have fallen behind schedule can catch up without having to start over. For school-age children who were not immunized when they were infants, or who have gotten behind schedule, a doctor or the local health department can provide information on how those children can be updated on their immunizations.
SOURCE: Centers for Disease Control and Prevention
In a study published in 1999, Salmon of Johns Hopkins found that, on average, people who claimed exemptions were 35 times more likely than vaccinated individuals to contract measles.
And the tendency of groups that opt out of immunization to settle in certain geographic regions doesn’t raise only those groups’ risk of contracting vaccine-preventable disease, he concludes. It also threatens the health of surrounding communities, placing at risk children who are too young to be vaccinated, people avoiding vaccines for medical reasons, and those for whom vaccines simply didn’t "take."
The largest numbers of unvaccinated children are clustered in counties in the states of California, Colorado, Illinois, Michigan, New York, Oklahoma, Pennsylvania, Texas, Utah, and Washington.
As Harvard’s Dr. McCormick puts it, "If you live in one of those states, near one of those communities, there’s no question you’re at greater risk.
"Look at Boulder, Colorado," she says, referring to a county with one of the highest rates of unvaccinated children in the country. "The people living in the counties around Boulder know where their pertussis comes from every year."
Just over 60 percent of all children ages 19 months to 35 months in the United States are fully vaccinated, according to federal data. But that success rate may not be stable, according to research led by the CDC’s Gust and published in Pediatrics this month.
From a 2001 survey of 2,315 households that had participated in the federal government’s National Immunization Survey, Gust concludes that vaccine-safety concerns are contributing "substantially" to the country’s problem of underimmunization.
What’s worse, she writes, is the finding that even parents who had their children fully immunized were worried about the potential side effects of those vaccines, "suggesting a risk to the currently high vaccination levels." "We have to stop expecting people to do this because we say so," Gust said in a recent interview. "We’re living in an era where we can’t rely on disease to prove to people that immunization is a good idea. We need to do a better job explaining to parents why this is a good idea."
Getting school health workers on board is critical to that effort, health professionals and researchers say.
A study in the June issue of Pediatrics—based on survey results from 594 schools in Colorado, Massachusetts, Missouri, and Washington state—found that trained nurses were more likely than other school personnel to be supportive of immunization, and that schools with trained nurses were the least likely to have students who claimed vaccine exemptions.
But the researchers, led by Salmon of Johns Hopkins University, also found that too many survey respondents who identified themselves as working with parents on immunization for their schools were misinformed about the value of vaccines. "Many school personnel seem to be unaware of the seriousness of some vaccine-preventable diseases and that unimmunized children are highly susceptible to diseases," the researchers conclude. "These misperceptions were associated with an increased likelihood of a child having an exemption."
Meanwhile, in Westchester County, Dr. Lipsman says he’s counting on schools to help prevent future outbreaks of dangerous disease. As whooping cough spread through the county this past school year, the health commissioner urged school health officials to review students’ immunization records carefully and pressure parents whose children lacked mandated vaccines to get them.
"The state does audits, but it doesn’t look at every child’s record," Lipsman says. "The rubber really meets the road at the schoolhouse."
Coverage of research is underwritten in part by a grant from the Spencer Foundation.
Vol. 23, Issue 43, Pages 26-29Published in Print: July 28, 2004, as Vexing Vaccines