August is a time for vacations, but also a time for back-to-school preparations including the required physicals and vaccinations. For the combined measles, mumps and rubella (MMR) vaccine, evidence shows a concerning trend of reduced immunization rates and increased incidence of disease.
It has been 15 years since the now-retracted article by former physician Andrew Wakefield linked the MMR vaccine to autism. An epidemiological study by the Institute of Medicine of the National Academies of Science found no connection between the vaccine and autism. Additional studies supported this conclusion. However from a public health standpoint, the damage has already been done. A reduction in childhood vaccination rates can allow immunization levels to fall below those needed for community immunity—when a large enough number of individuals are immunized to ensure that most of a group is protected, and diseases are less able to spread. Therefore, this reduction in immunization rates can increase the risk of a large, sustained measles outbreak.
Each state sets immunization policies for measles and other diseases for children attending public schools. All states allow medical exemptions and most states also allow exemptions on religious or philosophical grounds. The latter exemption group has grown in recent years, resulting in increased numbers of unvaccinated children and growing numbers of measles cases. The Centers for Disease Control and Prevention reported a total of 222 measles cases in 2011 compared with a median of 60 cases per year between 2001 and 2010. In 86 percent of the 2011 cases, patients were unvaccinated or had had unknown vaccination status.
Politicians are now attempting to mitigate disease risk through legislation. Washington and Vermont, among other states, are tightening exemption rules. Specifically, states are requiring philosophical exemptions to include a statement to be signed by a health care practitioner indicating that she provided the child's guardian with information about the benefits and risks of immunization for children.
Washington's new exemption rules went into effect in 2011, and this past school year the percentage of kindergarteners with complete immunizations rose above 85 percent according to the state health department. This level of immunization should promote community immunity to several diseases, including measles, mumps and rubella, based on CDC estimates. Data from additional states will tell whether this trend holds for other parts of the country.