June 23, 2014
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Two doses of varicella vaccine more effective than one

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A two dose regimen of varicella vaccine provided more protection than a one dose regimen among school-aged children, according to study findings in the Pediatric Infectious Disease Journal.

Carrie A. Thomas, PhD, of the West Virginia Department of Health and Human Resources, Charleston. W.Va., and colleagues assessed varicella cases that occurred in West Virginia public schools between January 2010 and May 2011, alongside vaccination information from schools, health departments and health care providers in the area. During the study period, 30 varicella outbreaks and 266 cases were reported from 30 schools in 17 counties. Cases with missing information were excluded, and the final study cohort consisted of 133 children with varicella and 365 of their classmates, who served as the control, with a mean age of 11 years. Type of varicella vaccine received was not recorded.

Overall, vaccine effectiveness was 83.2% (95% CI, 69.2%-90.8%) for one dose of varicella vaccine and 93.9% (95% CI, 86.9%-97.1%) for two doses. The incremental vaccine effectiveness (defined as two doses vs. one dose) was 63.6% (95% CI, 32.6%-80.3%) against all varicella. One dose vaccination was 88.2% (95% CI, 72.7%-94.9%) effective in preventing moderate and severe varicella, compared with two dose vaccination which was 97.5% (95% CI, 91.6%-99.2%) effective. The incremental vaccine effectiveness was 78.6% (95% CI, 40.9%-92.3%) for moderate and severe varicella.

Vaccine effectiveness of the one-dose regimen decreased as time increased, from 93% effectiveness less than 5 years after vaccination to 81.8% effectiveness 10 years after vaccination.

Both regimens had milder rash than unvaccinated cases. Rash severity decreased as the number of doses decreased. The proportion of mild rash decreased from 70% among children who received two doses; 49.1% among those who received one dose; and 24.6% among those with varicella who were unvaccinated.

No severe disease was found among children who received two doses.

“In varicella school outbreaks reported during 2010 to 2011, two doses of varicella vaccine conferred greater protection against all varicella and moderate/severe varicella than a single dose…These data, in addition to declines in varicella incidence and the reduced number and size of varicella outbreaks observed since the initiation of the two-dose varicella vaccination regimen, provide evidence of the greater effectiveness of two-dose varicella vaccination compared to the single dose regimen,” the researchers concluded.

Disclosure: The researchers report no relevant financial disclosures.