Lyme Disease Vaccine

by Food and Drug Administration (FDA)

Don C.'s hands hurt for months. He kept getting sore throats. When he turned his head to either side, it was painful to move it back. He suffered from a lack of concentration, memory loss, aching joints, and depression. Yet, the then-41-year-old New Jersey native just assumed it was all part of getting older.

As symptoms worsened, Don became concerned that he was suffering from far more than the effects of middle age. A diagnostic questionnaire and extensive testing eventually confirmed that he had Lyme disease.

In December 1998, the Food and Drug Administration licensed the first vaccine to help prevent Lyme disease, a bacterial infection transmitted by tick bites. LYMErix, distributed by SmithKline Beecham Pharmaceuticals, Philadelphia, is an unusual vaccine. Like most vaccines, it stimulates the human immune system to produce antibodies, in this case directed against Borrelia burgdorferi (B. burgdorferi), the bacterium that causes Lyme disease. But unlike typical antibodies that fight the bacteria in a person's body, animal experiments suggest that when a tick bites a vaccinated person, the vaccine-induced antibodies enter the tick and kill the bacteria there.

FDA emphasizes that the vaccine, however, is not 100 percent effective, and should not be considered a substitute for other standard preventive measures against infection, including wearing protective clothing, using tick repellent, and removing attached ticks (see accompanying articles).

"The vaccine's effectiveness depends on people receiving three doses over a one-year period," says Karen Elkins, Ph.D., an immunologist with FDA's Office of Vaccines, Research and Review. The initial dose is followed by a second dose one month later, and a third dose 12 months after the first.

The time of year the vaccination is given is important as well, Elkins stresses. Vaccine administration should be timed so that the second dose and the third dose are given several weeks before the beginning of the B. burgdorferi transmission season, usually April in the Northeastern United States.

FDA has approved the vaccine for people 15 to 70 years old who live or work in grassy or wooded areas, where infected ticks tend to thrive. But, although LYMErix may provide protection for most people, the vaccine does not prevent all cases of Lyme disease. It is also not known how long protection against Lyme disease lasts after vaccination.

The national Centers for Disease Control and Prevention says that people of all ages are susceptible to the infection, but that the highest reported rates of Lyme disease are in children 2 to 15 years old, and adults aged 30 to 55.

The Bite of a Tiny Tick

The most common carrier of Lyme disease in the United States is the deer tick (so named for its dependency on deer to reach the adult stage of its complex, two-year life cycle), or black-legged tick. The Western black-legged deer tick also transmits Lyme disease along the coasts of northern California, Oregon and Washington.

Ticks become infected with the Lyme disease bacteria when they feed on the blood of an infected animal — most notably, the white-footed mouse, white-tailed deer, other mammals, and birds — a method necessary for them to progress to each of three life-cycle stages.

According to CDC, ticks are usually in the nymph stage (between larva and adult) when they transmit Lyme disease to humans. Approximately the size of a poppy seed, the nymphs are most active between May and July. The spiral-shaped Lyme-causing bacterium, B. burgdorferi, enters the skin at the site of a bite and migrates until it penetrates the bloodstream. It usually takes at least 36 hours following a tick bite for the bacterium to be transmitted, so early removal of attached ticks is very important.

Although in theory Lyme disease could spread through blood transfusions or other contact with infected blood or urine, CDC says no such transmission has been documented. And there is no evidence that a person can get Lyme disease from the air, food or water, through sexual contact, or directly from wild or domestic animals.

While at least one definitive case of Lyme disease acquired by either a deerfly or horsefly was documented in The New England Journal of Medicine in 1990, CDC says that no convincing evidence exists that the disease can be transmitted by insects such as mosquitoes, flies or fleas.

In rare cases, CDC also says, Lyme disease acquired during pregnancy may lead to infection of the fetus, but the effects of such transmission on the fetus remain unclear.

Telltale Rash Not the Whole Story

Early-stage Lyme disease is usually marked by a telltale skin rash called erythema migrans, which appears three days to one month after the tick bites. It starts as a small red spot at the site of the bite. As it enlarges, the center of the rash may clear, resulting in a bull's-eye appearance. Common sites for the rash are the thigh, groin, trunk, and armpits. CDC estimates that 85 percent of people with Lyme disease get the characteristic rash.

The rash is often accompanied by flu-like symptoms, including fever, fatigue and muscular pain. Other early signs can include secondary skin lesions and facial paralysis.

Although early Lyme disease almost always responds to appropriate antibiotic therapy, if untreated or inadequately treated, the condition can progress weeks, months or years after the tick bite to late Lyme disease, which is characterized by distinctive arthritic, neurologic and cardiac problems.

Although a tick bite is an important clue for diagnosis, many people cannot recall having been bitten because the tick is so tiny and its bite is relatively painless. (The picture at right shows a normal size thumb with a deer tick nymph on it.) Therefore, NIH advises physicians to base their diagnosis not only on the history of a tick bite, but also the patient's symptoms and a thorough ruling out of other diseases that may have triggered those symptoms.

About the Author

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