In states where medical exemptions for school vaccinations are easier to get, exemption rates are higher, according to a new study published late last month in the Journal of Infectious Diseases.
Investigators from Emory University looked at state standards for medical exemptions from vaccination requirements for kindergartners. The study spanned seven school years, from 2004-2005 to 2010-2011, and found a nationwide total of 87,631 medical exemptions from kindergarten entry requirements. In states with more lenient requirements, they saw a significant increase in exemptions, compared to states with more stringent standards.
States with stricter rules on nonmedical exemptions (i.e. philosophical or religious reasons) also saw an increase in medical exemptions, which suggests that some parents seek medical exemptions when they are unable to obtain a nonmedical one.
"The appropriate use of medical exemptions is important to maintaining sufficient herd immunity to protect those who should not be vaccinated due to medical contra-indications," said Saad Omer, senior investigator of the study. "Medical providers, parents, school officials, and state health officials are responsible for ensuring that medical exemptions are actually medically indicated."
When most people are immune, infections are less likely to spread, and the chain of transmission is disrupted. Those with compromised immune systems – such as infants, cancer patients or people with immune disorders who should not be vaccinated – are protected by this “herd immunity.”
As more people opt out of vaccination, for medical or nonmedical reasons, a community’s ability to achieve herd immunity is compromised, and the most vulnerable members of the community are at increased risk for infection.
“Granting medical exemptions for invalid medical contraindications may promote unfounded vaccine safety concerns,” wrote Daniel Salmon and Neal Halsey of Johns Hopkins Bloomberg School of Public Health in an editorial commentary accompanying the Emory study. “Although states may wish to allow parents who make decisions based on poor science or perceptions to withhold vaccines from their children, these exemptions should be distinguished from valid medical exemptions.”
The Centers for Disease Control and Prevention recommend that all children receive the DTaP (diphtheria, tetanus, and pertussis, or “whooping cough”), IPV (polio), MMR (measles, mumps and rubella) and varicella (chickenpox) vaccines by the age of 6.
Diseases like measles, once considered eliminated in the United States, have recently seen a cascade of outbreaks bringing them back into the public spotlight. In a report published August 24 by the CDC, 76 percent of measles cases reported in 2011 in the U.S. among persons aged 16 months to 19 years, were among people not vaccinated for nonmedical reasons.
It is important to note, however, that children with an exemption are unlikely to be totally unvaccinated. According to the CDC, less than one percent of children received no vaccinations from 2006 to 2009. And among children with nonmedical exemptions, 75 percent had received at least one vaccine previously.