Case-Based Varicella Surveillance in the 2-Dose Vaccination Era -- Georgia, 2012

BACKGROUND:   Before licensure of varicella vaccine in 1995, varicella was a universal childhood disease causing approximately four million cases in the United States anually. Subsequent evidence of breakthrough infections, despite high levels of single dose coverage rates, led the Advisory Committee on Immunization Practices (ACIP) to recommend a second dose of varicella vaccine for children. Since 2007 Georgia has required all school-aged children be vaccinated with two doses of varicella vaccine prior to school entry. In 2011, the Georgia Department of Public Health (GDPH) added varicella to the state’s notifiable disease list, mandating health care providers report all varicella cases to public health. This report summarizes the first year of case-based varicella surveillance in Georgia.

METHODS:   Passive, case-based varicella surveillance was conducted by GDPH from January 1 through December 31, 2012. The Council for State and Territorial Epidemiologists (CSTE) standard varicella case definition of “an illness characterized by acute onset of a diffuse papulovesicular rash without other known cause” was used. A case was confirmed if it met the clinical case definition and was either epidemiologically –linked to another case or laboratory confirmed. A probable case met the clinical case definition but was not epidemiologically-linked, laboratory confirmed, or could not be reached for follow-up interview.  Probable and confirmed cases were entered into Georgia’s State Electronic Notifiable Disease Surveillance System (SendSS) and analyzed.

RESULTS:   In 2012, 172 varicella cases (44 confirmed and 128 probable) were reported in Georgia. Children ages 1 to 6 years of age accounted for 47.1% of varicella cases. Forty-nine cases received one-dose of varicella-containing vaccine, 64 received two doses, 12 reported previous history of disease, 42 were unvaccinated, and 5 had an unknown vaccination history. Among the 49 cases with one-dose of varicella-containing vaccine and reported disease severity, 67.4% reported mild disease (<50 lesions); 30.4% reported moderate disease (50-249 lesions); and2.2% reported severe disease (250-500 lesions).  Among the 62 cases with two doses of varicella-containing vaccine and reported disease severity, 71.0% reported having mild disease, 26.6% reported moderate disease; and 1.6% reported severe disease.

CONCLUSIONS:   GDPH must  achieve  consistent reporting for at least  3 years for data to be included in the National Notifiable Disease Surveillance System (NNDSS) and used to monitor vaccine impact. Varicella disease, although mild, was primarily reported in vaccinated individuals. The reason for this is unclear, but may indicate an increased awareness among vaccinated persons, and the need for laboratory confirmation to rule out false positive cases.