Objective: To quantify both the individual-level and attributable risk of varicella infection requiring medical care in children whose parents refuse varicella immunizations.
Design: Matched case-control study with conditional logistic regression analysis.
Setting: Kaiser Permanente of Colorado (KPCO) health plan between 1998 and 2008.
Participants: Each pediatric physician-diagnosed case of varicella (n = 133) was matched to 4 randomly selected controls (n = 493). Cases were matched by age, sex, and length of enrollment in KPCO. Main Exposures Varicella vaccine refusal.
Outcome measures: Varicella infection.
Results: There were 7 varicella vaccine refusers (5%) among the cases and 3 (0.6%) among the controls. Children of parents who refused varicella immunizations were at a greatly increased risk of varicella infection requiring medical care (odds ratio, 8.6; 95% confidence interval, 2.2-33.3) compared with children of parents who accepted vaccinations (P = .004). In the entire KPCO pediatric population, 5% of varicella cases were attributed to parental vaccine refusal.
Conclusions: Children of parents who refuse varicella immunizations are at high risk of varicella infection relative to vaccinated children. These results will be helpful to health care providers and parents when making decisions about immunizing children.