This is no time to get complacent about Lyme disease, the most common tick-borne illness in the country. Although the Food and Drug Administration licensed the first Lyme disease vaccine for people in December, we continue to have problems preventing this usually treatable but sometimes devastating bacterial disease. The three-dose vaccine is effective but not perfect, and disease-bearing ticks are expected to be unusually abundant this year.
Even if fully vaccinated, everyone who ventures outdoors in areas where ticks carrying the Lyme bacteria are likely to be present is at risk of contracting the disease and would be wise to observe all the usual precautions about preventing tick bites. These bacteria, spirochetes with the scientific name Borrelia burgdorferi, are typically carried by tiny deer ticks that feed on white-footed mice and lizards as well as deer, people and pets.
Approved With Reservations
The new vaccine, called Lymerix and marketed by SmithKline Beecham, was not greeted with unbridled enthusiasm by the F.D.A.'s advisory committee, which reluctantly recommended its approval. In fact, the head of the committee, Dr. Patricia L. Ferrieri of the University of Minnesota Medical School, said at the time, ''It's rare that a vaccine is voted on with such ambivalence and such a stack of provisos.''
The vaccine is highly unusual. It works by attacking the Lyme organisms while they are still in an infected tick; the attack occurs when the tick starts feeding on the blood of a vaccinated person. The vaccine triggers the production of antibodies to a protein called OspA on the coat of the spirochetes. It takes 24 to 72 hours of feeding time before the tick sends spirochetes through its saliva into an unsuspecting host. So as the tick begins to extract its meal of blood, antibodies from the vaccinated person are consumed along with it and kill the spirochetes before they reach the tick's saliva.
The vaccine is given in three doses -- the first two are a month apart and the third comes 11 months later -- at a total cost of about $150 (not including doctor fees). If just the first two doses are taken, the vaccine is only 50 percent effective in preventing Lyme disease. All three doses were shown in studies involving nearly 11,000 people to be 78 percent effective, and a more recent study by the manufacturer indicated that the vaccine works equally well if the third dose is given after six months.
This means, however, that even when people are fully vaccinated, about one person in five remains at risk of getting Lyme disease. Also, the immunity wears off with time, and booster doses, perhaps given annually, are likely to be needed.
Furthermore, since the tests for safety and effectiveness were conducted on people between the ages of 15 and 70, the vaccine has not yet been approved for use in children and the elderly. Nor was the vaccine tested in pregnant women, so it is not known if it is safe for them to be immunized. The manufacturer is now testing the vaccine in children 4 to 15 years of age, a group more likely than most adults to be cavorting in areas where ticks are found.
Another problem involves the ability to diagnose a case of Lyme disease accurately in a vaccinated person. The usual test, called Elisa, may appear positive even though the person is not infected, and doctors may have to use the more costly Western blot test.
There are also long-term safety concerns. The human immune system has a nasty habit of making mistakes; it sometimes produces antibodies to its own tissues, resulting in autoimmune diseases. The OspA protein on the spirochete's coat resembles a protein in the human body, and there is a real concern that in some vaccinated people, the immune system will begin attacking itself and spirochetes, resulting in an incurable illness requiring potent medications to control.
The F.D.A. advisory committee also has raised concerns about whether vaccinated people are at greater than average risk of acquiring treatment-resistant arthritis, neurological damage or heart disease, all of which can occur in people with severe untreated Lyme disease.
Long-term surveillance -- for a decade or more -- is needed to determine whether such risks exist, and so far vaccinated individuals have been followed for only a few years. The Centers for Disease Control and Prevention recommends against vaccinating people who have had treatment-resistant Lyme arthritis.
How to Protect Yourself
Lyme disease has been reported in 48 states. But Lyme-carrying ticks are most abundant in the Northeast, the upper Midwest and some parts of Northern California and the Pacific Northwest. For people who work or frequently play in wooded or overgrown grassy areas where Lyme disease and deer are common, the prevailing advice is that the benefits of vaccination outweigh any known or potential risks. Travelers to such areas may consider vaccination if they expect to experience frequent or prolonged exposure to tick habitat.
Perhaps the greatest risk of being vaccinated would be complacency about the chances of getting Lyme disease. Remember, the vaccine does not always work. Even if you are fully immunized, experts say that the usual anti-tick precautions are needed: cover up and use a tick repellent. When out in or around tick habitats, wear long sleeves and light-colored long pants with cuffs tucked into your socks. Spray your pants, socks and shoes with a tick repellent, like permethrin, and use Deet on exposed skin.
Pets can be protected with a repellent that is applied between the shoulders each month during tick season. It spreads across the skin and kills ticks before they can transmit Lyme disease. Ask your veterinarian what is best for your pet.
After every outing in tick-infested areas, take off all your clothes and check your skin for ticks. Also check your pets and children. In fact, making a family tick check a part of your daily routine is a good idea, because the prompt removal of ticks can help prevent infection. Deer ticks are very small and have elongated bodies (the more common wood ticks are larger and round). The deer tick, about the size of a poppy seed when it first attaches, enlarges as it feeds. Do not touch the tick when you remove it. Use a fine-pointed tweezer or a simple plastic spoon-like tool called Ticked Off, sold in some pharmacies and stores catering to outdoor activities.
Also pay attention to every red circular rash you may develop whether or not you have removed a tick from that area. A ''bulls-eye'' rash that often clears in the center as it spreads outward is the hallmark of a Lyme infection. So are flu-like symptoms. Arthritis, neurological symptoms and heart abnormalities occur weeks to months after infection, and are considered signs of late disease. So act fast. Get to a doctor without delay if you suspect infection.
Lyme disease is diagnosed definitively through a blood test, although waiting for the results can delay needed treatment. If Lyme disease is treated early with effective antibiotics, the debilitating, long-lasting consequences can almost always be prevented. Early cases are best treated with one of three antibiotics taken for 10 to 21 days: amoxicillin (500 milligrams three times a day), doxycycline (100 milligrams twice a day) or cefuroxime axetil (500 milligrams twice a day).
Map/Chart: ''Lyme Disease Risk'' Lyme-carrying ticks are most common in the Northeast, the upper Midwest and some parts of Northern California. Map of the United States highlights areas at high to low risk of lyme disease. (Source: Mortality and Morbidity Weekly Report, Centers for Disease Control and Prevention)