Volume 1, Number 1
Hepatitis A Cases Shelby County, Tennessee 1994-1996 |
(Memphis) The Memphis and Shelby County Health Department, in Memphis, Tennessee (county population 826,330), is now completing the largest vaccination program yet attempted for the control of a hepatitis A outbreak. According to health department epidemiologist Denise Sockwell, MSPH, since July 1995, over 24,000 children age 2-9 have been vaccinated in census tracts with the highest incidence rates.
Outbreak began in July 1994
Prior to the current outbreak, the largest recorded epidemic of hepatitis A in Memphis was in the early 1970s. The hepatitis A case rate began to increase again in July 1994. The County experienced 210 cases in 1994 and 1,538 in 1995, for a 1995 incidence rate of 186 per 100,000.
In 1995, cases were distributed along a bimodal age curve, with peaks in the 0-9 and 20-29 age groups. Of the 1995 cases, 89% occurred in African Americans (the county population is 44% African American). The highest attack rates occurred in the poor, inner city neighborhoods of Memphis. Over 240 persons were hospitalized in 1995, and one death was associated with HAV infection.
The outbreak consumed large amounts of personnel resources and immunoglobulin. Health department staff were diverted from other projects to work on the outbreak. In 1995, over 15,500 doses of immunoglobulin were used during contact investigations, in day care centers, and in public notifications for possible restaurant exposure.
After consultation with Tennessee State health officials and the Hepatitis Branch, CDC, the County decided to use the newly licensed hepatitis A vaccine (Havrix®, SmithKline Beecham Biologicals) in a mass immunization program. Previous outbreak control programs had been tried in rural areas in New York State, Alaska, and Butte County, California, but the Memphis program was the largest one to date, and the only one attempted in an urban area. Funding for vaccine purchase was obtained from the Tennessee Department of Health and from managed care organizations through TennCare, the Tennessee equivalent of Medicaid.
Mass vaccinations given in four zones
The vaccination program in Memphis was carried out in four successive zones. These were chosen from incidence maps to include neighborhoods with the highest incidence rates. Vaccinations in Zone 1 were conducted in August and October 1995, and vaccinations in the other three zones began about every 2-3 weeks afterwards. Children in each zone ages 2-9 were offered free vaccination with Havrix®, a three-dose series of 360 ELISA units each.
Over 24,000 children ages 2-9 were vaccinated. Vaccination coverage rates for each zone varied between 53% and 59%. Dr. John B. Kirkley, Interim Health Officer of the Memphis and Shelby County Health Department, instituted a hepatitis A vaccination mandate for all children in the four zones ages 2-9 who attended day care centers, Headstart, or pre-school programs. In these institutions, coverage rates were significantly higher.
Moderation of the outbreak?
The monthly incidence rate in Memphis has declined from 163 cases in October to 115, 108, and 105 cases in the succeeding three months (See chart). While the decline could be due to the vaccination program, officials are waiting for further data before drawing definitive conclusions.
In December, the Health Department reported that Zone 1 children in the 0-4 age group had experienced no new cases of hepatitis A after the vaccine was given. Prior to the vaccination campaign, the annualized incidence rate in that zone had been about 200/100,000 for the same age group. Preliminary analysis indicates that the program caused a significant decline in the incidence rate in vaccinated age groups, but little or no decline in unvaccinated age groups. The incidence rate in some unvaccinated age groups actually increased.
Previous theories of communitywide outbreaks have cast asymptomatic infected children age 0-5 as the primary transmitters to older children and adults. Analysis of the Memphis results will help establish whether toddlers are indeed the source of virus for older cases. Other outbreak control programs now underway in California and other states may also help answer this question. In Butte County, California, for example, hepatitis A vaccine was administered to several thousand schoolchildren ages 2-12 in 1995 during a large communitywide outbreak. Merck & Co. donated pre-licensed vaccine, VAQTA® for the project. Results from that study are pending.