Abstract
Epidemiological data regarding tetanus and diphtheria immunity in elderly people in Brazil are scarce. During the First National Immunization Campaign for the Elderly in Brazil in April 1999, 98 individuals (median age: 84 years) received one tetanus-dyphtheria (Td) vaccine dose (Butantan Institute, lot number 9808079/G). Inclusion criteria were elderly individuals without a history of severe immunosuppressive disease, acute infectious disease or use of immunomodulators. Blood samples were collected immediately before the vaccine and 30 days later. Serum was separated and stored at -20 degrees C until analysis. Tetanus and diphtheria antibodies were measured by the double-antigen ELISA test. Tetanus and diphtheria antibody concentrations lower than 0.01 IU/mL were considered to indicate the absence of protection, between 0.01 and 0.09 IU/mL were considered to indicate basic immunity, and values of 0.1 IU/mL or higher were considered to indicate full protection. Before vaccination, 18% of the individuals were susceptible to diphtheria and 94% were susceptible to tetanus. After one Td dose, 78% became fully immune to diphtheria, 13% attained basic immunity, and 9% were still susceptible to the disease. In contrast, 79% remained susceptible to tetanus, 4% had basic immunity and 17% were fully immune. Although one Td dose increases immunity to diphtheria in many elderly people who live in Brazil, a complete vaccination series appears to be necessary for the prevention of tetanus.
Highlights
The impact of routine childhood immunization on the epidemiology of many diseases is well known
As observed when categories of immunity were analyzed, geometric mean antibody values increased with one Td dose
Diphtheria geometric mean antibody concentrations were statistically higher than tetanus values before and after vaccination (P < 0.001 for both comparisons, t-test; Figure 1)
Summary
The impact of routine childhood immunization on the epidemiology of many diseases is well known. Many of these countries have realized that large segments of their adult populations are susceptible to diphtheria [2] as a consequence of the decrease in the asymptomatic carrier status of toxigenic Corynebacterium diphtheriae and of the natural boosters that used to occur in the pre-vaccination era. When the circulation of toxigenic strains of C. diphtheriae is reduced, repeated doses of diphtheria toxoid are needed to maintain immunity in the adult population [3]. Acquisition of immunity against other diseases has not changed with time: protection against tetanus, for instance, can only be achieved through vaccination of each individual and subsequent boosters are needed in order to maintain protective antibody levels [4]. Vaccination of the elderly population has been recommended as a routine in some countries [5]. Assessing immunity to vaccine-preventable diseases in the elderly is necessary in order to provide a correct immunization scheme
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