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September 21, 2023

The first Lyme disease vaccine in 20 years is nearly here, and others may be on their way

Cases of the tick-borne illness have surged in recent decades, prompting a push to develop new immunizations. A shot from Pfizer is in late clinical trials, and Penn Medicine is testing another

Prevention Vaccines
Lyme disease vaccines Erik Karits/

Lyme disease is spread by bites from black-legged deer ticks, causing long-term illness in 10-20% of cases. Vaccines have not been available for years, but drugmakers and other researchers say new shots can help prevent surging cases.

As Lyme disease becomes increasingly prevalent in the U.S., renewed attention has been given to developing vaccines that can protect people against the tick-borne illness.

Lyme disease shots have not been available since 2002, when the Lymerix vaccine was pulled off the market. Since then, Lyme disease cases reported in the U.S. have doubled, according to the U.S. Centers for Disease Control & Prevention. As many as 476,000 Americans are now diagnosed and treated each year for Lyme disease.

A new Lyme disease vaccine made by Pfizer and France's Valneva SE is now in Phase III clinical trials and may be available as soon as 2026. Several other vaccines are in the works, including one being developed by Penn Medicine. That vaccine, which uses the mRNA technology employed by COVID-19 vaccines, has been tested on animals with promising results.

The U.S. Food & Drug Administration approved the first Lyme disease vaccine, Lymerix, in 1998. At the time, Lyme disease was much less widespread. Getting vaccinated was viewed as a niche intervention for people in northeastern states, where black-legged deer ticks that spread the disease are most common. Safe outdoor habits and checking for insect bites, including the bull's-eye rash often associated with Lyme disease, were considered adequate forms of prevention for most people.

People who get Lyme disease most commonly complain of fatigue, joint pain and fever. They often can be treated with antibiotics and make full recoveries within a few weeks.

In about 10-20% of cases, complications can linger for months and years without relief. Those who develop post-treatment Lyme disease sometimes develop neurocognitive issues that interfere with their mental functioning. They often struggle to find effective medical care and turn to unproven remedies to manage a chronic condition that's still not well understood.

Despite its limited use, Lymerix was found to be about 75% effective at preventing illness. The flu shot ranges between 40-60% efficacy in preventing flu infections, for comparison.

Lymerix hit the market at a time when vaccine hesitancy was on the rise. A study linking vaccines to autism in children — now widely discredited and deemed fraudulent — had a considerable and lasting effect on public sentiment about vaccine safety. A resurgence of skepticism accompanied the development of vaccines and booster shots during the COVID-19 pandemic, reinvigorating efforts to stop the spread of misinformation at a time when new vaccines could emerge to help prevent common ailments, like Lyme disease. 

But Lymerix produced concerns of its own during the few years it was available. Some people who received the vaccine blamed their joint pain on the mechanism of the shot, which was designed to target a protein found on the bacteria that causes the infection. This hypothesis had been bolstered by some longtime Lyme disease researchers who were seeking to understand why arthritis affected so many sufferers.

The maker of Lymerix, SmithKline Beecham Plc, (now GlaxoSmithKline), was sued by groups of people who had received the vaccine. And even though regulators rejected the theory tying Lymerix to joint pain symptoms, the drugmaker wound up settling a number of class-action lawsuits. Lymerix's reputation was effectively destroyed. 

Other drug makers who had been considering applying to have Lyme disease vaccines approved chose to abandon their plans, believing the effort was not justified by the limited demand, according to a Bloomberg report about the possible comeback of Lyme disease vaccines.

The explosion of Lyme disease cases in the U.S. and globally has been linked to climate change, which is making some parts of the world more hospitable to ticks and others less so. Most Lyme disease infections happen during the summer when ticks are thriving and people are outdoors. On the East Coast and into the Midwest, longer summers have enabled ticks to spread their range. Growing populations of white-tailed deer also are considered contributing factor to the spread of the disease, although mice are more commonly the source Lyme transmission.

Increasingly, research suggests tick bites happen at home during outdoor play, gardening and yard work. They're not just a problem for hikers and people that work outdoors. As ticks breed, their tiny nymphs are capable of bites that can go unnoticed and may not leave rashes. The risk is more pervasive than many people realize.

Pfizer and Valneva SE are betting the explosion of Lyme disease will make a new vaccine more appealing to the public. Like the previous Lymerix shot, their vaccine targets the protein that's linked to the infection. The shot works by clearing the tick of the infection after it bites a person, thus preventing transmission of the infectious bacteria.

The key difference in the vaccines is that Pfizer's targets the protein in a way that is expected to reduce the risk of side effects.

And unlike Lymerix, the new vaccine would be approved for children and adolescents. People who already have had Lyme disease also could get vaccinated, because reinfection is possible with additional tick bites. How it works on such people is part of the research being done by Pfizer and Valneva.

Progress on the clinical trial stalled earlier this year when about half of the study participants were cut due to issues at U.S. sites, which were run by a third-party provider. Still, the companies said they expect the vaccine will be proven safe and effective when they seek approval from regulators.

"With increasing global rates of Lyme disease, providing a new option for people to help protect themselves from the disease is more important than ever," Annaliesa Anderson, head of vaccine research & development at Pfizer, said in August.

The Pfizer vaccine is the Lyme disease immunization nearest FDA approval. But there are at least eight other Lyme disease vaccines in development, according to GlobalData, a data and analytics company. 

Penn Medicine's vaccine potentially could provide longer-lasting protection against Lyme disease due to the use of mRNA technology, which in this case trains the immune system to recognize and respond to the infectious protein.

Vaccines that use mRNA technology also are being explored as possible cancer treatments and as a way to improve the reliability of flu shots.  

"The mRNA technology shows great promise for use in developing a vaccine that may prevent Lyme disease and subsequent development of the debilitating symptoms," said Norbert Pardi, a Penn Medcine microbiologist who helped test the vaccine.

What remains to be seen, years after vaccine hesitancy helped kill Lymerix, is whether the pandemic's effects on public trust will continue to hamper receptiveness to getting shots.

"You will never be able to convince them. It was true 20 years ago, and it's still true today," Valneva CEO Thomas Lingelbach told Bloomberg. "And so our approach is an approach of education and communication."

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