Breakthrough Chicken Pox: An Old Disease With a New Look

Jessica C. Stovel, RPh


March 05, 2013

In This Article


How does chicken pox present in children vaccinated against varicella? Is the course of the disease the same? How should it be managed?

Response from Jessica C. Stovel, RPh
Adjunct Assistant Professor, Department of Psychiatry, Division of Child and Adolescent Psychiatry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada

Prior to use of the varicella vaccine, there were an estimated 4 million cases of varicella each year in the United States. In the early 1990s, the highest incidence occurred in children aged 1-4 years, likely due to the increased exposure resulting from a higher frequency of childcare use. Since the introduction of the varicella vaccine in 1995, however, the overall incidence of varicella has declined by approximately 90%.[1]

Cases of breakthrough varicella have been documented to occur in up to 15%-20% of vaccinated children, even in populations of children with good immunization rates.[2,3,4,5] Breakthrough disease has been hypothesized to occur because the vaccine may provide only a partial protection, and/or immunity may wane over time.[5]

Breakthrough Disease

Breakthrough varicella accounts for more than 50% of the reported varicella cases in communities with high vaccination coverage.[1] One case-control study examined 339 eligible varicella-vaccinated children aged 13 months or older who were clinically diagnosed as having varicella and who also had a positive polymerase chain reaction testing for varicella-zoster virus DNA. Each case subject was matched with 2 controls by age and pediatric practice. The study found a statistically significant adjusted overall varicella vaccine effectiveness of 87% (P < .001). Of note, there was a significant difference in the vaccine's effectiveness in the first year after vaccination (97%) compared with that observed in years 2-8 after vaccination (84%, P = .003),[3] which may lead credence to the theory of waning immunity across time.

In addition, vaccine efficacy in the first year after vaccination was significantly lower when the vaccine was administered at younger than 15 months of age (73%) compared with those children vaccinated at 15 months of age or older (99%, P = .01). Most cases of breakthrough disease were mild. The vaccine's effectiveness against moderate or severe disease was 98% (P < .001).[3]