Investigators found higher rates of whooping cough in such states to the tune of around 50 percent higher than in states which only allowed exemptions for medical reasons and religious beliefs. The researchers have reported their findings in the Journal of the American Medical Association.
Study authors, led by Saad B. Omer of Johns Hopkins University in Baltimore found that in states such as California, parents can take a personal-belief exemption by simply signing a school immunization form. Still other states, like Maryland, officially allow only religious exemptions; but here too parents have only to sign a form, which makes it likely that many take the exemption for personal reasons.
Omer said that the elevated rates of whooping cough in these states point to the "very real consequences" of relaxing vaccination requirements.
Whooping cough, also known as pertusis is a highly contagious bacterial infection of the respiratory system which causes fits of severe coughing and breathing difficulties -- often with a distinctive "whoop" sound on inhalation. Although a person can become infected at any age it is especially dangerous, and potentially fatal, to babies and young children.
Although childhood vaccination with the combined diphtheria, tetanus and pertussis or the DPT vaccine can prevent whooping cough, the rate of infection in the U.S. has been steadily rising in recent years.
According to Dr. Daniel A. Salmon, an associate professor of epidemiology at the University of Florida College of Medicine and the study's senior author this trend is one reason why the current study was undertaken.
All U.S. states require children entering school to have proof they've received standard vaccinations, though all also grant exemptions for medical reasons. In addition, nearly all states also allow exemptions for religious beliefs, while 19 grant waivers for personal beliefs.
The study found that in these latter states an increasing number of parents have been opting out of vaccination in recent years. On an average, the rate of non-medical exemptions grew by 6 percent per year between 1991 and 2004.
Salmon reported that parents usually claim such exemptions on the grounds of concerns about vaccine safety. His earlier studies have shown that 69 percent of those parents who sought exemptions did so because they feared vaccination did more harm than the diseases it prevents.
These concerns mostly stem from proposed link between the MMR vaccine and autism, a link which has now been refuted by several international studies.
Salmon and his colleagues argue that states should have "administrative controls" that make non-medical exemptions more difficult to obtain. This, Salmon said, could look something like the process of becoming a conscientious objector to the draft.
He explained that the government would either have to demonstrate an "overwhelming need" for universal vaccination or grant the exemption.