Health impact of measles vaccination in the United States.

As a result of intensive efforts to vaccinate children, measles and its attendant complications of encephalitis and death have declined more than 99% from the prevaccine era. Similarly, subacute sclerosing panencephalitis has declined markedly. Measles vaccine has been demonstrated to be extremely safe, as well as extremely effective. The health and resource benefits due to vaccination against measles during the first 20 years of vaccine licensure have been enormous. In this period it is estimated that vaccination against measles has prevented 52 million cases, 5,200 deaths, and 17,400 cases of mental retardation, achieving a net savings of $5.1 billion. These substantial health and resource benefits of measles vaccination will continue to accrue in the future.

Impact of measles in the United States.

Measles has had a severe impact on children in the United States since colonial times. In the early decades of the 20th century, thousands of fatal measles infections were reported each year. During the 1950s an annual average of greater than 500,000 cases of measles and nearly 500 deaths due to measles were reported in the United States. Surveys indicated that 95% of the population had been infected with measles by the age of 15 years. The introduction of measles vaccine and its widespread use, which began in 1963, has had a major impact on the occurrence of measles in the United States. Reported numbers of cases, deaths due to measles, and complications of measles (e.g., encephalitis) have declined dramatically. Accompanying the decline in reported incidence of measles and following it by approximately seven years, has been a decline in the reported incidence of subacute sclerosing panencephalitis (SSPE). In recent years, the incidence of measles has dropped to levels that are less than 1% of those seen in the prevaccine era. In 1981, provisional figures indicated that only 10% of counties in the United States reported any cases of measles. The reported incidence in 1981 was 1.3 cases per 100,000 population, compared with an average incidence of 336.3 cases per 100,000 population in the decade 1950-1959. Thus, the impact of measles in the United States has been markedly reduced, and it is anticipated that indigenous transmission will be eliminated entirely from the country within the year.

Elimination of indigenous measles from the United States.

In October 1978, a nationwide initiative to eliminate indigenous measles from the United States by October 1, 1982, was announced. The measles elimination program has three major elements: attaining and maintaining high immunization levels, aggressive and effective surveillance, and vigorous response to cases. In 1980, immunization levels in children entering school for the first time were 96%, indicating that the necessary levels have been attained in the age group. Mechanisms are in place to assure maintenance of these levels; these rely heavily on the use of immunization requirements for school attendance in each state. Aggressive surveillance systems have been developed for each state to detect suspected measles cases as soon as possible after they occur and to investigate them within 24 hr of notification. The clinical definition of measles used is fever of greater than or equal to 101 F (38.3 C); rash of three or more days duration; and cough, coryza, or conjunctivitis. The response to outbreaks involves identifying persons in the area who are at risk of contracting measles, determining those who are possibly susceptible, and ensuring that these persons are vaccinated. In school outbreaks, susceptible students are vaccinated or excluded from school until the outbreak is over. During 1981, measles morbidity reached a record low level of only 3,032 reported cases (provisional total). Epidemic measles occurred in only a few outbreaks of limited size and duration, and endemic cases were restricted to a small number. Imported cases averaged slightly more than two per week, occasionally producing limited outbreaks, but more often resulting in no secondary spread. Transmission of measles has been interrupted in most of the United States. With continued vigorous implementation of the current strategy and with additional measures to lessen the risk of importations, it appears likely that the goal to eliminate indigenous measles transmission will be attained by October 1982.