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Sib's Chickenpox Vaccine May Protect Infants, Too
The varicella vaccination program in the United States may be indirectly benefiting infants too young to get the vaccine directly, according to the results of a prospective study.
Varicella incidence among infants younger than 12 months declined by 89.7% from 15.6 cases per 1,000 infants in 1995 (95% CI 13.5 to 18.2) to 1.6 cases per 1,000 infants in 2008 (95% CI 1.0 to 2.6). The decline followed an increase in varicella vaccination coverage, reported Sandra S. Chaves, MD, and colleagues from the CDC.
Distribution of varicella disease incidence according to age group also changed following implementation of the vaccination program. In 1995, the disease incidence was higher among those ages 1 to 10, followed by infants, and then adolescents between 10 and 14 years old. By 2008, disease incidence was similar among all age groups, according to the results, which were published in the December edition of Pediatrics.
"After implementation of the varicella vaccination program in the United States in 1995, a remarkable decline in varicella morbidity and mortality was documented," wrote the authors. "A community-based varicella active surveillance project in the United States provided investigators with the opportunity to examine 14 years of data (1995 to 2008) that could be used to better describe the epidemiology and clinical presentation of varicella disease in infants."
Active surveillance projects were put in place in Antelope Valley, Los Angeles County, Calif., and West Philadelphia, Pa. in 1995. Over 300 reporting units checked in every two weeks with information on any varicella cases that were identified. A structured interview was then conducted with the parent/guardian to collect demographic, clinical, and epidemiologic data.
From 1997 to 2008, statistically significant differences in the clinical presentation of the disease were seen, with infants five months or younger generally having milder disease compared to those ages 6 to 11 months.
A lower proportion of younger infants had 50 or more lesions (49% versus 58%, P=0.036), fewer had fevers of 38º C (100º F; 12% versus 21%, P=0.012), fewer had disease-related complications (6% versus 14%, P=0.01), and fewer were prescribed antibiotics (8% versus 14%, P=0.044).
Most of the hospitalized cases (10 of 15, 67%) were in the older infant group. The rate, however, did not differ according to age group (28.6 per 1,000 infant case-patients in the younger group versus 29 per 1,000 in the older cohort).
"Through reducing varicella disease exposures, the varicella vaccination program in the United States has provided substantial benefits to infants who are too young to be vaccinated," wrote the authors. "Catch-up varicella vaccination and high uptake of the herpes zoster vaccine among older age groups will further reduce infection risk and protect those who are not eligible for varicella vaccination."