Undervaccination is an “increasing trend,” according to a 2013 study analyzing data on 323,247 children aged two to 24 months. Close to half did not receive all recommended vaccinations or were not vaccinated according to recommended schedules.1 This growing trend has serious repercussions. In 2013, 189 people had measles—the second largest number of cases in the US since measles was eliminated in 2000.And in California, voluntary undervaccination was one of the causes identified in the 2010 pertussis outbreak that was responsible for 9,120 illnesses and 10 deaths.3

Below, Maria Carillo-Marquez, MD, a specialist in pediatric infectious disease and Assistant Professor, Department of Pediatrics. Sanford Children’s Specialty Clinic, University of South Dakota, discusses why undervaccination is on the rise and how she approaches the concerns raised by parents regarding vaccinations.

Why do you think there is an increase in the number of parents refusing to vaccinate their children?

Many are victims of misinformation from the media, celebrities and bad science, suggesting that vaccines are dangerous. Parents have also become complacent, assuming that diseases such as measles and pertussis have been permanently eradicated. They are more scared of the vaccines than they are of the diseases and don’t understand the concept of “herd immunity.” This vulnerability especially affects immunocompromised children.

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Are parents concerned about the connection between vaccines and autism?

The most common concern I hear is that the measles-mumps-rubella (MMR) vaccine, which contains thimerosal, causes autism. When this comes up, I describe the history of the autism controversy beginning with the now-debunked study that appeared in The Lancet in 1998,and describe the extensive research that supports the safety of the vaccination.

Why do parents request alternative vaccination schedules?

Many worry that their child’s immune system will be overloaded. I explain that from the moment of birth, a baby is exposed to a huge number of antigens. Vaccines contain only a tiny proportion of what a baby is exposed to naturally. Moreover, spacing the vaccinations too far apart increases the duration of susceptibility to the disease, without safety or efficacy data to support the proposed timetable. The reason for the number of shots, especially for inactivated vaccines, is that immunity to the antigen is built in phases until it reaches the protective level. For live vaccines, the antigen reproduces and spreads throughout the body. One dose typically produces a satisfactory immune response, but a second dose assures the immunity because not all children respond to the first.