Whooping cough rates higher in states where vaccination exemptions easily obtained

Whooping cough is re-emerging nationwide and youngsters in states that permit parents to easily opt out of vaccinating their children are at increased risk from the disease, researchers from Johns Hopkins University and the University of Florida report Oct. 11 in the Journal of the American Medical Association.

States that readily grant exemptions or offer personal belief exemptions have about 50 percent higher rates of pertussis, more commonly known as whooping cough, after adjusting for a large number of demographic variables.

"By demonstrating an association between state policies and pertussis, we highlight the very real consequences of relaxing school immunization requirements," said Saad Omer, M.B.B.S., M.P.H., an assistant scientist of international health at the Johns Hopkins Bloomberg School of Public Health and the study's first author.

All states require documentation that children entering school have met the requirements, which include vaccines to protect against diseases such as diphtheria, measles, polio and pertussis.

But all states also permit medical exemptions to immunization requirements, and most allow exemptions based on religious beliefs. Many offer a broader exemption based on personal belief that may be granted for religious, philosophical or other nonmedical reasons.

"This really adds a new piece of information in our effort to control pertussis," said Daniel Salmon, Ph.D., an associate professor of epidemiology in the University of Florida College of Medicine and the study's senior author.

Recently, several states also have sought to expand nonmedical exemptions.

"Our study shows an increase in the number of children exempted in states that make exemptions widely available," Omer said.

Researchers at the two academic health centers and at the Centers for Disease Control and Prevention examined long-term data on state-level exemption rates at school entry and the incidence of pertussis for individuals 18 years or younger. They found that nonmedical exemption rates were higher and increasing in states that permitted exemptions based on personal belief and in states where exemption processes were less arduous. Those states also were strongly associated with higher incidence of pertussis.

Pertussis - a highly contagious but preventable disease - is endemic in the United States. According to the CDC, the incidence of the disease has increased nationwide in the last 20 years, with 25,827 cases reported in 2004, the most recent data available.

Pertussis is caused by a toxin produced by a bacterium that is spread easily through person-to-person contact, coughing and sneezing. It is more severe in infants and young children, who consequently have a greater risk of pneumonia, seizures, encephalopathy (a brain disorder) and other potentially deadly complications.

In a study published last year, the researchers found the No. 1 reason why parents refuse vaccines and claim exemptions are concerns about vaccine safety, despite strong scientific evidence that vaccines are extremely safe.

"There are also differences between parents of vaccinated and unvaccinated children in perceived susceptibility to and severity of (vaccine-preventable) diseases, perceived efficacy of vaccination and trust in their government," Salmon said.

Children who are not vaccinated are at increased risk of contracting disease and passing it on to others. Among those vulnerable are children too young to be vaccinated, those with a valid medical reason for not vaccinating or those who are vaccinated but have not had a sufficient immunological response to fight off the disease. Protection in people who are vaccinated decreases over time, in what health experts call "waning immunity."

Walter Orenstein, M.D ., associate director of the Emory Vaccine Center and former director of the CDC's National Immunization Program, said the research highlights the need for public health officials to remain vigilant.

"This study is important because it raises concerns that our safety net for preventing outbreaks of vaccine-preventable diseases, school immunization laws, may be eroding in some states," said Orenstein, who was not involved in the study.

The researchers propose that a balance be struck between parental autonomy and public health mandates. Health-care professionals and public vaccine information campaigns need to do a better job at risk communication for parents who have real concerns, and the exemptions must be more difficult to obtain, the authors said.