Study confirms that 2 vaccine doses protect against varicella

A second dose of varicella vaccine is much more effective than 1 dose in preventing varicella (chicken pox) in children.

In June 2006, the US Centers for Disease Control (CDC) recommended routine administration of a second dose of varicella vaccine to children 4 to 6 years old (or at least 3 months after the first dose) and a second catch-up dose to older children. This second dose was recommended after breakthrough cases of varicella in immunized children and continuing outbreaks of varicella among children were discovered despite high rates of vaccination with a single dose. The CDC made the single dose recommendation after the US Food and Drug Administration licensed the vaccine in 1995.

As reported in the Journal of Infectious Diseases, active surveillance of pediatric practices in southern Connecticut uncovered 71 cases of varicella in children 4 years or older. None of the children had received 2 doses of vaccine, 93% had received 1 dose, and 7% were unvaccinated.

Although breakthrough varicella generally is milder than varicella in children not immunized, the researchers noted that breakthrough varicella still can be transmitted, leading to outbreaks in schools and day care centers.

In an editorial, David W Kimberlin, MD, professor in the department of pediatrics, and codirector, division of pediatric infectious diseases, University of Alabama at Birmingham, noted the hundreds of outbreaks of breakthrough varicella annually in the late 1990s and early 2000s, before the CDC's recommendation for a second dose. The study is the "first to evaluate the effectiveness of 2 doses of varicella vaccine in a 'real-world' setting." He wrote, "The high effectiveness of 98.3% found in this investigation supports the programmatic change instituted 4 years ago."

Shapiro ED, Vazquez M, Esposito D, et al. Effectiveness of 2 doses of varicella vaccine in children. J Infect Dis. 2011;203(3):312-315.

Kimberlin DW. Control of varicella disease, version 2.0. J Infect Dis. 2011;203(3)297-299.