Dogs have a Lyme disease vaccine, so why don't humans?

Growing up in rural Pennsylvania, I was often warned by adults to be careful of ticks if I ever played outside. Like so many other children, the main tick-related boogeyman that I was taught to fear was the dreaded Lyme disease. Readily identifiable by the angry red bullseye rash it often leaves on patients, Lyme disease can also cause severe headaches, fever, shooting pains, muscle and joint aches, facial palsy, which is drooping of one or both sides of the face, and nerve pain.

Lyme is also a disease for which — if you're a dog — there is a vaccine. Humans, however, are not so lucky, which raises provocative questions about why we don't have a cure for a disease that, according to some estimates, infects nearly half a million Americans each year. Yet COVID-19 vaccines were developed in less than a year from the virus first came to international attention.

Furthermore, the problem seems to be getting worse, as many experts agree that human-caused changes to the environment are likely to make ticks a big problem for humanity going forward. As such, it would seem necessary to at least explore the possibility of a human vaccine for Lyme disease. So what gives?

"There was previously a vaccine for humans. In fact, one of the vaccines for dogs is very similar to the prior human vaccine," Dr. Linden T. Hu, a professor of immunology at Tufts Medical School, told Salon by email. Unfortunately, the human vaccine, which was called LYMERix, suffered from low sales due to the need for three doses and a yearly booster. It was eventually withdrawn from the market due to what the Centers for Disease Control and Prevention (CDC) described as "insufficient consumer demand."

Even if LYMERix had stayed widely available, however, Hu noted that the vaccine also suffered from "imperfect efficacy of protection and a concern that was raised over the possibility of the vaccine causing an autoimmune arthritis (which later proved to be unfounded.)"

Lyme disease expert Dr. Tania T. Dempsey wrote to Salon that the history of that vaccine and its difficulties has been widely discussed in medical literature, if for no other reason than in the two decades since the vaccine's withdrawal "it has become apparent that Lyme disease cases are on the rise and there is an urgent need for a human vaccine."

Dempsey outlined the three types of products being considered, including a Lyme vaccine called VLA15, which is now in phase 3 trials and "uses a similar method to the previous vaccine by targeting the outer surface protein A (OspA) of Borrelia burgdorferi, the bacteria that cause Lyme disease."

Another, known as "Lyme PrEP," is a "pre-exposure prophylaxis," which means it offers protection before encountering the virus. It's similar to a medication used for treating the HIV virus. Lyme PrEP is only at a very early stage of clinical testing. known as phase 1, but if it worked would be a monoclonal antibody that could be given to a person as a shot that kills the bacteria in a tick's gut before the human is infected.

Finally, there is the 19ISP mRNA vaccine, also in an early stage of development, which makes it impossible for a tick to attach to a human by helping the immune system recognize a tick's saliva and also causes enough sensation that the person is likely to notice being bit. Ticks are specially evolved to be extremely stealthy, so their victims may not notice being bit for days.

All three of these present different strategies for defending against Lyme, but many questions still exist about this enigmatic disease.

"There is still much to be learned about Lyme disease," Dempsey pointed out. "It is a complex bacterial infection with different stages of effects on the human body and we are still learning about all the possible complications that can ensue."

Indeed, Lyme disease may be an illness that a patient must reckon with for their entire life, developing chronic symptoms in what is known as Chronic Lyme Disease or Post-Treatment Lyme Disease syndrome.

"This is an area of controversy but recent research supports the presence of persister forms of Borrelia burgdorferi resistant to standard antibiotic treatment," Dempsey explained. "There is currently an active search for new drugs or repurposing of old ones for targeting chronic, persister infection."

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Hu, while reiterating that the Pfizer human vaccine is in Phase 3 and is similar to the previously approved vaccine, added that for the new vaccine to succeed it "requires fewer doses and protects for longer than one year. Vaccines that prevent against other diseases that can be co-transmitted with Lyme disease would also be useful."

One might also add that it needs to be capable of rapid mass production, analogous to what the United States pulled off during the COVID-19 pandemic. Experts already anticipate that as climate change worsens, ticks are going to expand their range — and tick-borne illnesses like Lyme disease will become more prevalent.

"Over the last 20 to 30 years, tick populations around the world have been expanding their geographic range, and the warming of the planet is prolonging tick season in many places causing an increase in the prevalence of tick-borne disease like Lyme disease," Wendy Adams, research grant director at the Bay Area Lyme Foundation, told Salon by email. Indeed, there are practical consequences to how this expansion in the ticks' range will impact the spread of the diseases that they so often carry.

"Since humans and dogs are not important to the lifecycle of the causative organism for Lyme, vaccines will not affect the increase in geographic range we are seeing and the risks that people face year after year," Hu explained. "To affect those, we would need to control the infection in the ticks, mice and birds that carry the disease in the wild."

Until that happens, humans need to follow best practices if they are bitten by a tick to protect themselves from any diseases that the insects may carry. Adams elaborated on what the Bay Area Lyme Foundations recommends once someone can confirm they have been bitten by a tick. First and foremost: Get tested.

"That way, you will know the potential pathogens that could have been transmitted, depending on the length of time the tick was attached," Adams explained. "This is important because some pathogens are not treated by antibiotics, and they would require a different drug regimen. It's important to note that ticks can be so tiny that they are missed, and sometimes the tick you see is not the one that infected you."