Two Doses of Chickenpox Vaccine Better Than One

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Children, roll up your sleeves. Experts say that two doses of chickenpox vaccine will better protect children against this infectious disease than one dose. The findings of the collaborative team effort between Yale and Columbia University supports the two-dose approach recommended in the United States since 2006.

One dose of chickenpox vaccine is not good enough

Between 1995 and 2006, children aged 1 to 13 years could usually count in receiving a single dose of varicella vaccine, per recommendations from the Centers for Disease Control and Prevention (CDC). According to a report from the CDC published in September 2008 in Pediatrics, this approach was 80 to 85 percent effective in preventing disease overall, and more than 95 percent effective in preventing severe varicella.

The one-dose approach also reduced disease incidence by 57 to 90 percent, hospitalizations by 75 to 88 percent, and deaths by more than 74 percent. However, outbreaks of chickenpox continued to occur, even among highly vaccinated populations of school children. Therefore in 2006, the CDC made a change in the vaccination program and recommended that a second dose of varicella vaccine be administered to children 4 to 6 years old.

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In this new study, Eugene D. Shapiro, MD, and colleagues performed active surveillance in a region of Connecticut and uncovered 71 cases of chickenpox in children aged 4 years or older. None of these children had received the recommended two doses of vaccine, 66 (93%) had received one dose, and 5 had never been vaccinated.

Using a case-control study design, the investigators then compared the effectiveness of two versus one dose of vaccine. The results showed one dose to be 86 percent effective compared with 98.3 percent for two doses. Overall, “the odds of developing varicella were 95 percent lower in children who had received two doses of the vaccine compared with those who had received only one,” said Shapiro.

For now, it appears two doses of chickenpox vaccine are better than one. The authors note, however, that “there should be continued monitoring of the effectiveness of two doses to assure that its high degree of effectiveness is sustained.” For families that cannot afford vaccinations for their children, the Vaccines for Children Program may be able to help.

SOURCES:
Centers for Disease Control and Prevention
Marin M et al. Pediatrics 2008 Sep; 122(3): e744-51
Shapiro ED et al. Journal of Infectious Diseases 2011 Feb; 203:312-15

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