The Complicated Reason There's No Lyme Vaccine + 2 Promising Treatments In The Works

Warm weather brings ticks, and with ticks comes Lyme disease, the fastest-growing vector-borne disease in the U.S. In fact, around 476,000 Americans1 are diagnosed and treated for Lyme every year—a stat that's frightening enough to make any of us tuck our pants into our socks before hitting the hiking trail. 

While Lyme disease is finally getting some visibility as a major health threat that can lead to chronic and debilitating symptoms if undetected, there's no great way to prevent it other than to not get bitten by the tiny ticks that carry it. And so, every spring and summer people begin asking the same question: Why the heck don't we have a Lyme vaccine yet? After all, your dog can get vaccinated, so why can't you? 

The answer is complicated—turns out, there was a Lyme vaccine called LYMErix2 available for a hot minute about 20 years ago, but it was pulled from the market amid concerns of side effects, and nothing came to replace it. That is, until now. Separate groups of researchers are actively studying two preventive treatments: a new Lyme vaccine and a Lyme pre-exposure prophylaxis (PrEP) shot, both of which could be available within two to four years.

In 1998, the LYMErix vaccine was rolled out by SmithKline Beecham (now GlaxoSmithKline). It was a three-part vaccine that was found to be about 76% effective3 against Borrelia burgdorferi, a corkscrew-shaped spirochete bacterium that causes Lyme disease. It was intended for people 15 to 70 years old living or working in areas with high rates of Lyme disease. 

The LYMErix vaccine caused the immune system to generate antibodies against B. burgdorferi—specifically, against a protein on the outer surface of the bacteria called outer surface protein A (OspA). These Lyme-killing antibodies worked in a unique way: When a tick bit a vaccinated person, it ingested the person's blood and antibodies, which traveled into the tick's gut, where the antibodies destroyed the bacteria before it ever entered the human body. 

So what was the problem? Soon after the vaccine was introduced, reports began trickling in about pretty intense side effects, including arthritis, neurological symptoms, and cognitive issues. And in 1999, a class-action lawsuit was filed against SmithKline Beecham (SKB) by 121 people who had received the vaccine. They claimed that SKB knew and failed to adequately warn doctors and patients that certain people may be genetically predisposed to developing autoimmune arthritis in response to the vaccine, and they wanted SKB to update the vaccine's safety warnings to mention arthritis. 

Lyme disease itself can cause arthritis, so the claims about LYMErix raised a lot of questions. While the vaccine did not contain live bacteria and thus couldn't cause Lyme disease, people began to worry about its approach to generating antibodies against OspA. Why? Around this same time, scientists discovered that people with a certain genetic variant (HLA type DR4+) were more likely to develop arthritis after getting Lyme disease. They were also more likely to generate autoantibodies (antibodies that mistakenly target your own cells) in response to OspA. Because of this Lyme-OspA-autoimmunity connection, experts considered the possibility that LYMErix might also cause arthritis in patients with the DR4+ variant.

But in 2001, an FDA advisory panel concluded that there wasn't sufficient evidence to support claims2 that LYMErix caused adverse events, including arthritis. By that time, 1.4 million doses of the vaccine had been distributed and the Vaccine Adverse Events Reporting System (VAERS) database included only 59 reports of arthritis associated with the vaccine—a number that experts said was in line with the rates of arthritis in unvaccinated individuals. Even so, SKB pulled the vaccine from the market in 2002, citing low demand resulting from all of the unfavorable media coverage caused by the lawsuits. 

The vaccine, called VLA15, is being developed by French biotech company Valneva in collaboration with Pfizer—it's the only active vaccine in clinical development against Lyme and has fast-track designation from the FDA. Like LYMErix, it targets the outer surface protein A (OspA) of Borrelia bacteria and generates antibodies that can kill Borrelia within the tick's gut before it's transmitted to the human body. 

But this new vaccine may be useful in more geographic regions, where different strains of Borrelia bacteria are known to cause Lyme disease (not just Borrelia burgdorferi). "The key difference is VLA15 targets six strains of Lyme/Borrelia, whereas LYMErix only protected against one," says Purvi Parikh, M.D., clinical assistant professor at NYU Grossman School of medicine and immunologist with Allergy & Asthma Network. "With these six strains covered, it can be effective against 98% of Lyme disease." 

Research on the new vaccine appears promising so far. Findings from Phase 2 clinical trials suggest that a 3-dose series of the VLA15 elicits a functional immune response against the six strains and is generally safe across all age groups tested. Studies were conducted in areas where Lyme is prevalent, and even participants with a history of Lyme disease appeared to fare well during the trials. The vaccine will soon be studied in children ages 5 to 17, too.  

As for how effective this vaccine is or how long it lasts—we just don't know yet. "VLA15 has been studied in Phase 1 and Phase 2 trials, which have focused primarily on dosing, safety, and tolerability of the vaccine," says Jerica Pitts, director of global media relations for Pfizer. "The efficacy of the vaccine will not be fully understood until further trials are undertaken." 

A different type of shot, called Lyme PrEP, is being developed by infectious disease expert Mark Klempner, M.D., and a team of researchers at the University of Massachusetts Medical School. 

Unlike a vaccine, which triggers your immune system to make its own antibodies over the course of several weeks, the Lyme PrEP shot delivers a preformed anti-Lyme antibody directly into the bloodstream (providing passive immunity4)—meaning, it may be effective immediately upon injection. From there, it takes a similar approach to the vaccine: "When [the tick] drinks blood that contains this antibody, it immobilizes and kills the bacteria in the tick, so the transmission to you is blocked," Klempner explained in a recent interview.

Without all clinical trial data, it's impossible to answer this question, but Klempner believes Lyme PrEP may come with less risk of side effects. That's because it uses a single antibody to provide protection, unlike a vaccine that prompts the body to make many antibodies—not all of which provide protection, and some of which may cause side effects. Klempner's team used data from LYMErix studies to help them home in on the one highly effective antibody used in Lyme PrEP.

"Lyme PrEP may also be more helpful for immediate exposure, or for high-risk groups that either don't tolerate vaccines due to allergies or who don't respond to vaccines well," says Parikh. "Some people with weakened immune systems can't respond to vaccines, so we rely on passive immunity4 for them more often." 

Some doctors who treat Lyme disease are hesitant to express much excitement until more safety data is made available. "The potential concern is autoimmunity," says William Rawls, M.D. "These [approaches] apparently have similarities to the previous vaccine. I would assume researchers are paying close attention to the presence of autoimmunity in participants." So, as far as being optimistic, he says, "We just have to wait and see."

Keep in mind, LYMErix was never proved to cause autoimmune issues such as arthritis, but some questions still remain about its safety across different populations.

Raphael Kellman, M.D., a New York City–based integrative physician who also treats Lyme disease, does believe these preventive shots could have a lot of promise, for some. "Certainly for people in high-risk areas, these could be a good idea," he says. "But not for the masses. It's not going to be a panacea, so people will still need to take other precautions."

On that note, even if proved safe and effective, there's still one big reason that neither of these shots would ever be an all-around magic bullet: co-infections. "Ticks carry hundreds of bacteria, and most people with the chronic form of Lyme disease are also found to have co-infections with a variety of other microbes, including babesia, bartonella, rickettsia, anaplasma, and ehrlichia," says Rawls. "Many experts feel that the symptoms of Lyme disease may be driven by microbes other than Borrelia. If this is true, the vaccine will not eliminate the illness."