L. Allen, T. Lewis, C. Martin, M. Jones, C. Lo, M. Stamp, Texas Tech
G. Mundel and A. Way, Lubbock City Health Department
The number of measles cases in the United States has risen dramatically in the last few years. In 1983, the number of measles cases was at an all time low, 1497 reported cases, but in 1988, there were 3411 cases and in 1989 there were approximately 17,850 cases (Centers for Disease Control 1990). The state of Texas reported the second highest number of cases in 1989 (3201 cases) and one of the worst outbreaks in the United States occurred in the Houston area (1802 cases reported from late 1988 to September 1989) (Centers for Disease Control 1990; Canfield 1989). This increased incidence of measles in recent years has resulted in new recommendations for measles vaccinations in the United States. The Immunization Practices Advisory Committee (ACIP) has recommended two doses of measles vaccine for all children, the first dose at 15 months of age and the second when the child is about to enter school at kindergarten or first grade (Immunization Practices Advisory Committee 1989). (Previously, only one vaccination at 15 months of age was recommended.)
Some theoretical studies have confirmed the need for a higher rate of immunity from measles than that achieved by a single vaccination given during the first two years of life (Hethcote 1983, 1988). These investigations are based on the analysis of epidemiological models of SEIR type (S-Susceptible, E-Exposed, I-Infectious, R-Removed). Analyses of these models have provided a theoretical foundation for studying many questions related to the spread of an epidemic (Anderson and May 1979; Bailey 1975; Greenhalgh 1990; Hethcote 1976, 1983, 1988; Hethcote and Yorke 1984; Hoppensteadt 1975; May 1986; McLean and Anderson 1988; Waltman 1974).
In this report, SEIR models (stochastic and deterministic) are applied to a specific epidemic in a university setting. Data from a 1989 measles epidemic that occurred on the campus of Texas Tech University in Lubbock is thoroughly investigated. Calculations from the data and simulations of the models provide an estimate of the level of immunity that is necessary in this university population to prevent a measles epidemic.
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