Between 2011 and 2012, the United States experienced one of the largest pertussis epidemics in more than 50 years. Virtually every state was affected and 20 deaths from pertussis were reported. The state of Washington, which has one of the highest non-medical vaccine exemption rates in the country, was particularly hard hit, with 71.3 cases of pertussis per 100,000 person-years reported.
The best way to prevent pertussis in infants is by receiving the full series of pertussis-containing vaccine. Specifically, whereas protection against pertussis following one dose of DTaP (diphtheria-tetanus-acellular pertussis) is about 46 percent effective at preventing pertussis, receipt of three doses in the first six months of life is about 91 percent effective.
To determine whether the pertussis epidemic in the state of Washington had any impact on vaccination rates, researchers at Seattle Children’s Hospital and the University of Washington measured immunization rates for DTaP in infants before, during and after the epidemic (Wolf ER, et al.“Impact of a Pertussis Epidemic on Infant Vaccination in Washington State ,” Pediatrics 2014. Sep;134(3):456-64). They wanted to determine whether the pertussis epidemic compelled more parents to vaccinate their children against pertussis. The authors found “no significant difference in statewide up-to-date status with a pertussis-containing vaccine between pre-epidemic and either epidemic or post-epidemic time points.”
One could reasonably argue that people are compelled by fear more than reason. And that one of the main reasons that some people don’t vaccinate their children, or don’t vaccinate them on time, is that they simply don’t fear vaccine-preventable diseases. In other words, vaccines have become a victim of their own success. If this is true, then one might predict that recent outbreaks of diseases such as measles, mumps and pertussis would compel more parents to vaccinate their children. The study done in Washington State suggests that, if that reasoning is correct, current outbreaks either haven’t been large enough or frightening enough to change behavior.