Some parents have expressed concern that children are getting too many vaccinations, and the risks may outweigh the benefits. A recent paper from researchers at Kaiser Permanente of Colorado reported that the chickenpox (varicella) vaccine is the most commonly refused childhood vaccine. Parents who skip this vaccination express views that this infection is not serious and not likely to affect children today. For the first concern, the authors noted that before the varicella vaccine was licensed in 1995, the United States had approximately 4 million cases of chickenpox per year, with 10,000 hospitalizations and 100 deaths. For the second concern, the authors performed a study of 86,993 children enrolled in their managed care health plan between 1998 and 2008.
Chickenpox is certainly not as common today as it was when I was a child. The study identified 343 children with a diagnosis out of the 86,993 in the cohort, which is less than half of one percent. However, the history of smallpox vaccination demonstrates that vaccine-preventable diseases need not affect even one child. When vaccination rates are high enough, the disease dies out. This phenomenon is often called “herd immunity”.
One barrier to achieving herd immunity is the fact that not everyone has a perfectly functioning immune system. Thus, no vaccine yet has been able to protect 100 percent of the individuals who receive it. A second barrier is the fact that some children are medically ineligible for vaccines, because of illness or because they are not yet old enough for their full set of shots. A third barrier is parental refusal of vaccines for personal reasons.
The Kaiser researchers designed their study to see whether unvaccinated children are at significantly higher risk for chickenpox in a group where most children are vaccinated. They identified 133 children with confirmed diagnoses of chickenpox and vaccination records. For comparison, they chose 493 controls with similar demographics but no chickenpox.
The results: the chickenpox group contained 5.3 percent unvaccinated children, while the control group contained only 0.6 percent unvaccinated children.