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October 10, 2006

High Rates of Pertussis Found in States with Easy Immunization Exemptions

Saad B. OmerStates that easily permit parents to opt out of vaccinating their children for nonmedical reasons are at increased risk of pertussis (whooping cough), according to a new study from researchers with the Johns Hopkins Bloomberg School of Public Health, the University of Florida and the Centers for Disease Control and Prevention (CDC). States that easily grant exemptions or offer personal belief exemptions have higher nonmedical exemption rates than states that offered only religious exemptions. The study is published in the October 11, 2006, issue of the Journal of the American Medical Association.

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. Pertussis, which is characterized by severe coughing, is endemic in the United States. The incidence of the disease has increased nationwide in the last 20 years, with 25,827 cases reported in 2004, according to the CDC.

“In states that make exemptions widely available or easy to obtain, there has been an increase in the number of children who were not immunized. This is a disturbing trend; previous research has shown that school immunization requirements have played a major role in controlling vaccine-preventable diseases in the United States,” said Saad B. Omer, MBBS, MPH, lead author of the study and an assistant scientist in the Johns Hopkins Bloomberg School of Public Health’s Department of International Health.

The researchers examined long-term data on state-level exemption rates at school entry. They also analyzed the incidence of pertussis for individuals 18 years of age or younger from 1986-2004 for the 48 states that permit nonmedical exemptions and the District of Columbia. The study authors 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 were also strongly associated with a higher incidence of pertussis.

“Our results add a new piece of information in our effort to control pertussis,” said Daniel Salmon, PhD, senior author of the study and an associate professor of epidemiology in the University of Florida’s College of Medicine. “A reduction in the number of U.S. children receiving school immunizations hinders one of our most effective methods in preventing outbreaks of vaccine-preventable diseases,” added Salmon, who is also an adjunct associate professor in the Bloomberg School’s Department of International Health.

In their study, the researchers propose that a balance be struck between parental autonomy and public health mandates. Not only should public vaccine information campaigns be directed at parents who have real concerns, but exemptions should be more difficult to obtain.

In a May 2005 article published in the Archives of Pediatrics and Adolescent Medicine, Salmon and colleagues reported that parents who requested immunization exemptions perceived vaccines to be unsafe and ineffective, despite strong scientific evidence to the contrary. They also believed their children were less susceptible to vaccine-preventable diseases and that the diseases were less severe. Parents of exempt children also had low levels of trust for the government.

“Nonmedical Exemptions to School Immunization Requirements: Secular Trends and Association of State Policies With Pertussis Incidence” was co-authored by Saad B. Omer, William K. Y. Pan, Neal A. Halsey, Shannon Stokley, Lawrence H. Moulton, Ann Marie Navar, Mathew Pierce and Daniel Salmon.

The study was partially funded by a grant from the Centers for Disease Control and Prevention. In addition, co-authors received payment for consultant work or testimony on behalf of (unrelated to the current study) Sanofi Pasteur, GlaxoSmithKline, Merck, Chiron and the U.S. Department of Justice.

University of Florida Health Science Center News & Communications: Tom Fortner at 352-273-5814.

Public Affairs media contacts for the Johns Hopkins Bloomberg School of Public Health: Kenna Lowe or Tim Parsons at 410-955-6878 or paffairs@jhsph.edu.