Children who miss one or more of their scheduled whooping cough shots face a much greater risk of catching the potentially deadly disease, a new study shows. Risk jumps substantially with each delayed or skipped shot: children denied all recommended shots are 30 times more likely to get sick.
The results, published online Monday in JAMA, reflect a growing tendency among parents to delay or refuse certain childhood vaccinations. More than 10 percent of parents now “under-vaccinate” their kids, citing concerns about vaccine safety. Despite ongoing education campaigns to dispel misguided fears about vaccines, some parents still worry that too many vaccines “overwhelm” a young child’s immune system while others believe that specific vaccines can cause autism in healthy children. Neither is true.
Whooping cough (also known as pertussis) causes violent, spasmodic coughing fits that produce the disease’s trademark “whoop” as victims desperately struggle to breathe. Babies too young to vaccinate are at greatest risk of serious complications, as the infection quickly overwhelms their immature bodies. Last week, two newborns died in Texas during one of the biggest whooping cough epidemics there in 50 years. Pertussis can also cause seizures, brain damage and mental retardation as infection robs tissues of oxygen.
During the 2010 California epidemic—the largest in 60 years—more than 9,000 people contracted pertussis, and ten infants died. Of 159 pertussis deaths reported to the CDC between 2004 and 2011, nearly half were babies under three months old. To protect babies too young to get vaccinated, health officials urge pregnant women to get a booster shot during the third trimester.
Veering from a Science-Based Schedule
The Advisory Committee on Immunization Practices sets the childhood immunization schedule based on evidence-based approaches to reduce vaccine-preventable diseases. The ACIP recommends that children receive five doses of the DTaP shot—a diphtheria, tetanus and aceullar pertussis combination vaccine—between the ages of two months and six years.
Parents worried about vaccine safety have increasingly adopted alternatives to these well-studied schedules, choosing to delay, space out or forgo shots altogether. None of these options has been studied to understand just how they affect disease risk.
Toward that end, epidemiologist Jason Glanz and a team of health experts from across the country evaluated the consequences of delaying or refusing a child’s DTaP vaccination amid ongoing pertussis outbreaks. The team reviewed the medical records of children born between 2004 and 2008 at eight managed care organizations from coast to coast, including Kaiser Permanente Northern and Southern California. They identified confirmed cases of pertussis, then determined whether children were under- or fully vaccinated.
As expected, the more DTaP shots missed, the higher the risk. Missing or delaying three doses made a child 19 times more likely to get pertussis. Under-vaccinating for all four scheduled shots made a child 30 times more likely to get pertussis. More than a third of pertussis cases in kids ages three months to three years old could have been prevented if they'd received their shots on time.
It’s not surprising that deviating from the recommended schedule places children at much greater risk of getting a serious infection, says Glanz, an investigator with the Institute for Health Research at Kaiser Permanente Colorado. “The problem is that there are a lot of parents who think it’s okay to push [the vaccinations] off. They need to know that pushing them off places their children at risk, especially at a time when the disease is particularly serious.”
Theories without Evidence
Glanz and his colleagues didn’t interview parents for this study, so it’s not clear why they chose not to vaccinate their children against a disease that kills mostly babies. In another study, Glanz found that although parents typically trust their pediatricians for most medical advice, they think doctors don’t provide “balanced” information about vaccination risks and benefits. For information on risk, parents rely on other parents, web sites, advocacy groups, celebrities, and books that advocate alternate schedules and raise unfounded fears about vaccine dangers.
Fears about the pertussis vaccine surfaced in the early 80s, after the TV documentary “Vaccine Roulette” blamed the vaccine for leaving children dead or brain-damaged. The original vaccine contained the whole (killed) pathogen and so delivered hundreds of antigens to trigger an immune response. More antigens meant broader protection against numerous strains of the pathogen, but also produced more side effects, including febrile seizures, irritability, and a short-lived though frightening condition (called hypotonic hyporesponsive syndrome) that makes children limp and unresponsive.
Studies found no support for long-term brain damage or other terrible dangers raised by “Vaccine Roulette,” but many parents, understandably scared by what they saw, stopped vaccinating their children. Pertussis has been on the rise ever since, but not simply because parents shun vaccination. Public health officials attribute part of the increase to better recognition of the symptoms, now that the disease is common again, along with waning immunity and the evolution of more aggressive pathogens. To alleviate fears about the whole-cell vaccine, manufacturers created the current acellular version (DTaP) with just three antigens. Though DTaP is extremely effective in infants and young children, as Glanz’s study makes clear, it can’t target all circulating pathogen strains and wears off over time, which is why public health officials recommend booster shots for kids entering seventh grade.
The JAMA study paints a disturbing picture that many parents believe vaccines are more dangerous than an infectious disease that once killed 9,000 people a year. But it also shows that the childhood DTaP vaccine works. “Whatever concerns we have about the vaccine’s effectiveness, this study shows it prevents a lot of cases of serious infection without hurting kids,” says Roger Baxter, co-director of Kaiser Permanente’s Vaccine Study Center in Oakland. Baxter wasn’t involved in the study.
Although the childhood immunization schedule protects against more pathogens than ever before—thanks to discoveries that led to new vaccines—shots today elicit an immune response with just a fraction of the antigens present in older vaccines. That’s what vaccines are all about, says Baxter: protecting children against a disease by inducing an immune response without producing the illness. “It’s just sad that some people are afraid of it.”
Glanz wants parents to know that public health experts are on their side. “We know parents want to do what’s best for their child, and that’s our objective too,” he says. “Public health experts do studies like this not because we’re pro-vaccine but because we’re pro-child. We know these decisions can be difficult and there’s a lot of confusing information out there. We want to help parents make the best decisions for their child.”