Varicella Vaccine, Breakthrough Varicella, and Duration of Immunity

Abstract & Commentary

By Hal Jenson, MD, Chief Academic Officer, Baystate Health Professor of Pediatrics and Dean of the Western Campus of Tufts University School of Medicine, is Associate Editor for Infectious Disease Alert.

Dr. Jenson is on the speaker's bureau for Merck.

Synopsis: Surveillance data from 1995-2004 showed that the risk of breakthrough varicella after a single childhood vaccination dose increased significantly with the time since vaccination. A second dose of varicella vaccine, recommended for all children since June 2006, is expected to improve protection from waning vaccine-induced immunity.

Source: Chaves SS, et al. Loss of vaccine-induced immunity to varicella over time. N Engl J Med. 2007;356:1121-1129.

From community-based active surveillance data in Antelope Valley, California, (northeast of Los Angeles) from 1995-2004, 9.5% (1,080 subjects) of all 11,356 subjects with varicella had onset of rash > 42 days after varicella vaccination, which defines breakthrough varicella. The diagnosis was confirmed by physician evaluation or laboratory test in 770 subjects (71.3%). Children 8-12 yrs of age who were vaccinated > 5 yr previously were significantly more likely to have breakthrough varicella than those vaccinated < 5 yr previously (risk ratio, 2.6; 95% CI, 1.2 to 5.8). The annual rate of breakthrough varicella increased from 1.6 cases per 1000 person-years (95% CI, 1.2 to 2.0) within one year after vaccination to 9.0 cases per 1000 person-years (95% CI, 6.9-11.7) at 5 years and 58.2 cases per 1000 person-years (95% CI, 36.0 to 94.0) at 9 years. The age of disease at onset was the only factor associated with disease severity.

Commentary

These data demonstrate that the immunity induced by a single varicella vaccination during childhood wanes over time and is accompanied by increased incidence of breakthrough varicella that correlates with the time since vaccination. Waning immunity to varicella vaccination is a potentially serious concern because the postponement of varicella from childhood to adolescence and especially adulthood is accompanied by a much higher risk of severe complications.

Varicella vaccination with the live attenuated live virus vaccine containing the Oka strain was implemented in 1995 with a single dose for all children from 12 months of age to their 13th birthday, and 2 doses for persons >13 yrs of age. A single dose of vaccine in young children results in serologic evidence of immunity in 80%-85% of vaccinees. Clinical data suggest that a second dose of varicella vaccination for children may overcome primary vaccine failure, and also increases the proportion of children with protective antibody titers and enhances cellular immune responses. In June 2006 the Advisory Committee on Immunization Practices recommended that all children between 4-6 yrs of age receive a second dose of varicella vaccine, and also that all children, adolescents, and adults who have previously received only one dose of varicella vaccine receive a second dose. There is no long-term data on the duration of immunity from 2 doses of varicella vaccine in childhood.