2-Dose Varicella Vaccine Having Substantial Effect

Steven Fox

October 07, 2013

The incidence of varicella, as well as hospitalizations and outbreaks associated with it, has declined significantly since a 2-dose vaccine regimen was instituted in 2006, according to an analysis of active surveillance areas in California and Pennsylvania.

"Declines in incidence across all ages, including infants who are not eligible for varicella vaccination, and adults, in whom vaccination levels are low, provide evidence of the benefit of high levels of immunity in the population," write Stephanie R. Bialek, MD, MPH, from the National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia and coauthors. The researchers published their results online October 7 in Pediatrics.

Single-dose varicella vaccination for children was introduced in the United States in the mid-1990s and has been associated with dramatic declines in incidence, hospitalizations, and deaths.

In 2006, the Advisory Committee on Immunization Practices recommended a second dose in hopes of further quelling the disease. Although it has been generally believed that the addition of the second dose would increase efficacy, there has been scant evidence to substantiate that assumption.

Therefore, Dr. Bialek and colleagues assessed 1995-2010 epidemiologic data from 2 active surveillance areas: Antelope Valley, California, and West Philadelphia, Pennsylvania.

By 2010, varicella incidence in Antelope Valley was 0.3 cases per 1000 individuals compared with 1.1 in 2006 (a 76% decline). In West Philadelphia, the incidence had declined to 0.1 per 1000 individuals from 0.4 cases (a 67% decline). Both surveillance areas showed 98% decreases in varicella cases since 1995, the authors say.

In addition, the investigators report, the incidence of varicella decreased among all age groups after introduction of the second dose, including those individuals not eligible to receive the vaccine, such as infants.

By 2010, 61.7% of patients in both Antelope Valley and West Philadelphia had received a single dose of the vaccine, whereas just 7.5% had received 2 doses.

Vaccination also appeared to curb the severity of the disease. Of patients who received a single dose of the vaccine, but nevertheless contracted the disease, 62.8% had 50 lesions or fewer. Of comparable patients who received 2 doses of the vaccine, 70.3% had fewer than 50 lesions. The difference in the number of lesions between the 2 vaccine regimens was not statistically significant.

The 2-dose regimen also appeared to reduce the risk for hospitalization: Varicella-related hospitalizations declined more than 40% during 2006-2010 compared with 2002-2005, and by more than 85% compared with 1995-1998.

Further evidence of the positive effects of the 2-dose regimen is that only 12 varicella outbreaks occurred in Antelope Valley during 2007-2010 compared with 47 during 2003-2006 and 236 during 1995-1998 (P < .01).

The authors emphasize the importance of broadening vaccine coverage. "Full implementation of varicella vaccination recommendations across all age groups, including adolescents, adults, and women postpartum, remains critically important for ensuring the greatest possible protection of susceptible individuals at risk for severe varicella disease," they conclude.

This study was funded through a cooperative agreement with the Centers for Disease Control and Prevention. The authors have disclosed no relevant financial relationships.

Pediatrics. Published online October 7, 2013. Abstract


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