Varicella Cases Down, Breakthrough Cases Up.

BALTIMORE -- The incidence of varicella cases and hospitalizations dropped by about 80% between 1995 and 2000 in several areas of the country being monitored by the Centers for Disease Control and Prevention, Dr. Jane Seward reported in a poster presentation at the annual meeting of the Pediatric Academic Societies.

The greatest drop was among children aged 1-4 years, but declines were seen in all age groups, said Dr. Seward of the CDC in Atlanta.

In another presentation, Dr. Karin Gail of the CDC reported that the proportion of breakthrough cases of varicella is increasing at these sites, although there is no evidence of waning immunity.

The three sentinel surveillance sites--Antelope Valley Calif.; West Philadelphia, Pa.; and Travis County Tex.--have been monitored since 1995 to evaluate the impact of the live attenuated varicella vaccine. Reports of varicella cases come from schools and preschools, child care centers, physicians, public health clinics, large employers, and households.

Vaccine use is monitored through the Vaccine for Children Program and estimates of coverage are based on the National Immunization Survey.

Vaccine coverage in preschool children in these areas increased from 40% in 1997 to about 70% in 1999. Reports of varicella cases from 1995 to 1998 varied from year to year "and showed marked springtime seasonality," Dr. Seward said. But since 1999, there has been a marked reduction in cases and hospitalizations "with an attenuation of seasonality."

By 2000, about 20%-30% of the reported cases were in people who had been vaccinated. "With evidence of reduced transmission of varicella zoster virus in communities with moderate levels of vaccine coverage, it is increasingly important to vaccinate all susceptible children," she noted.