Lyme disease is caused by Borrelia burgdorferi, a tick-borne spirochete. More than 90 percent of cases of Lyme disease occur in the northeast, middle Atlantic and upper midwest regions. Although the most characteristic finding early in the disease is a skin lesion that usually appears three to 30 days after the tick bite, other symptoms, such as flu-like illness, lymphadenopathy and multiple lesions of erythema migrans, are also common. A single treatment with antibiotics cures early Lyme disease in over 90 percent of patients. If treatment is not initiated early, musculoskeletal, neurologic and cardiac symptoms may develop. About 60 percent of untreated patients develop frank arthritis that may be resistant to treatment with antimicrobial drugs. The first vaccine for prevention of Lyme disease in humans has been labeled by the U.S. Food and Drug Administration for use in patients 15 to 70 years of age. Consultants for The Medical Letter on Drugs and Therapeutics reviewed the data on the effectiveness and safety of this new vaccine.

The vaccine is made from a recombinant outer surface protein of B. burgdorferi. Antibodies produced in response to the vaccine destroy spirochetes in the gut of the engorged tick before they can be transmitted to the human host. A 20-month randomized study published in 1998 evaluated about 11,000 persons living in endemic areas who had received three doses of the vaccine at zero, one and 12 months. The vaccine was 76 percent effective in preventing symptomatic disease and 100 percent effective in preventing asymptomatic disease after three injections. By eight months after the third injection, antibody levels had fallen to near the lower limit of protective levels. In some unvaccinated patients, development of chronic antibiotic-resistant Lyme arthritis has been associated with high levels of antibodies to the OspA protein used in the vaccine.

The vaccine is generally well tolerated; the main adverse effect appears to be soreness at the injection site. Myalgia and flu-like illness with fever and chills usually occurred in the first two days after vaccination and typically lasted for no more than three days. The manufacturer recommends giving the vaccine intramuscularly in three doses at zero, one and 12 months, although antibody titers have been equivalent when the third injection was given either two or six months after the first dose. Ideally, the third dose should be administered in March before the start of the tick season.

The Medical Letter consultants conclude that Lyme vaccine is effective and well tolerated, although its long-term safety is a concern. It is unknown at this time whether long-term immunity will be retained or whether frequent booster injections will be necessary. It is recommended that use of this vaccine be limited to persons at high risk.