Lyme Disease Vaccines

Lyme disease is the most common tick-borne disease in the United States; 16 455 cases were reported in 1996 [1], and the actual incidence may be 10-fold higher [2]. In areas with a high incidence of Lyme disease, the licensing of vaccines against the causative spirochete, Borrelia burgdorferi, has been anticipated with great enthusiasm by the medical community and the general public. Two recombinant vaccines, each containing 30 µg of outer surface protein A (OspA), are in the final stages of approval by the U.S. Food and Drug Administration (FDA). The SmithKline Beecham product (LYMErix) contains an aluminum adjuvant, whereas the Pasteur Merieux Connaught product (Imulyme) does not. In studies in adults, 96% of participants showed a fourfold increase in antibodies against OspA antigen 2 weeks after receiving a second dose of either vaccine [3], although clinical trials have indicated that a third dose is necessary to further boost antibody levels and provide a protective efficacy of more than 80%. Diminished efficacy was noted in persons older than 65 years of age [4, 5].

The vaccines protect in a novel manner. Animal studies strongly indicate that the OspA antibodies elicited by the vaccines prevent human infection by neutralizing the spirochetes in the gut of the vector tick between the time of attachment and the subsequent transmission of B. burgdorferi to the host [6-8]. This unique mechanism of action suggests that development of effective neutralizing antibody levels is the critical determinant of vaccine efficacy. An additional protective effect may occur in the host's bloodstream, although B. burgdorferi undergoes substantial antigenic change, resulting in repression of OspA expression when in contact with warm blood.

The safety profile in vaccine trials that included more than 10 000 persons 15 years of age and older is highly …