Background: In Antelope Valley (AV), California, high varicella vaccine coverage led to declines in varicella incidence of 75% and 98% from 1995 through 2000 and 2010, respectively. Changes in herpes zoster (HZ) epidemiology are also expected with varicella vaccination. We reported previously that during 2000-2006 in AV HZ incidence decreased by 55% in children aged <10 years, while among 10-19 year-olds it increased by 63%, without a conclusive explanation for the increase. We update the analysis with 4 additional years of data.
Methods: Population-based active surveillance was conducted for HZ among AV residents <20 years old during 2000-2010. Telephone interviews and medical chart reviews collected demographic, varicella vaccination/history, and clinical data. We calculated HZ incidence for 2007-2010 and assessed trends since 2000.
Results: Among children age <10 years, HZ incidence declined 67% in 2010 compared with 2006, from 19 cases reported in 2006 (35.1/100,000 persons) to 7 reported in 2010 (11.7/100,000 persons) (p=0.025); between 2000 and 2010 HZ incidence declined 84%. Among 10-19 year-olds, HZ incidence decreased 32% from the 2006 peak of 65 reported cases (98.3/100,000) to 39 reported in 2010 (66.7/100,000 persons) but the trend was not significant (p=0.202) as the decline was primarily due to a lower rate in 2010; between 2000 and 2010 HZ incidence increased 12%, with substantial fluctuation in annual rates. We also found an increase over time in the interval between varicella and subsequent HZ among 10-19 year-olds with history of varicella.
Conclusion: During a period with high 1 dose varicella vaccine coverage and low varicella circulation enhanced by a 2 dose program in 2007, the decline in HZ incidence reported previously among children age <10 years continued. Among 10-19 year-olds, the increase reported through 2006 did not continue and incidence was at a slightly lower level by 2010; our findings weaken the external boosting hypothesis as a possible reason for the increased incidence previously reported in this age group. Widespread use of varicella vaccine could reduce HZ burden among vaccinated populations. Continued monitoring of HZ incidence is needed to detect changes in HZ epidemiology in the varicella vaccine era.
J. Zhang, None
A. Abraham, None
R. Harpaz, None
L. Mascola, None
S. R. Bialek, None
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