A lab-stage mRNA vaccine has shown promising results for preventing the spread of Lyme disease, the most common vector-borne disease in the United States. The vaccine was highly effective in guinea pigs, and researchers hope it will prove to be effective in humans too, reports Alice Klein for New Scientist.
According to the Centers for Disease Control and Prevention (CDC), the number of reported cases of Lyme disease has doubled since 1991 and continues to grow, fueling the need for a vaccine. Several are in early trials, but this one is the first to use mRNA technology, which is used in the Pfizer-BioNTech and Moderna Covid-19 vaccines, reports Nicoletta Lanese for Live Science. In fact, the study was done in collaboration with Drew Weissman, a physician and scientist at the University of Pennsylvania, who co-invented mRNA vaccines.
Humans contract Lyme disease from the bite of a blacklegged tick, which carries the bacteria Borrelia burgdorferi. For the bacteria to be transmitted, the tick must latch onto the skin for 36 to 48 hours, according to the CDC.
Most vaccines target a specific pathogen—like SARS-CoV-2 or influenza—but this one doesn't. Instead of targeting B. burgdorferi, the vaccine trains the immune system to respond to tick saliva, reports Ed Cara for Gizmodo. The results of the trial were published this week in the journal Science Translational Medicine.
"All human vaccines directly target pathogens. This would be the first vaccine that does not target the pathogen," co-author Erol Fikrig, an epidemiologist at Yale, tells Gizmodo via email. "Rather by targeting the tick, you prevent the transmission of a pathogen. In this case the Lyme disease agent."
The snippets of mRNA in the vaccine code for 19 different proteins found in ticks' saliva, which will trigger the body to produce those proteins and elicit an immune reaction. By training the immune system to respond to the saliva instead of the bacteria itself, it shrinks the time that ticks spend feeding on a host; consequently, that will reduce the likelihood that the tick transmits B. burgdorferi since it takes at least 36 hours to do so, reports Live Science.
In the trial, the researchers latched Lyme-ridden ticks on two sets of guinea pigs: one that received the vaccine and the unvaccinated control group. The ticks were removed once the guinea pigs started developing inflammation or rashes, usually around 18 hours later, reports New Scientist.
The vaccinated guinea pigs developed an immune reaction, such as redness and inflammation, much faster than the non-immunized group, according to a press release.
"The vaccine enhances tick recognition, partially turning a tick bite into a mosquito bite," Fikrig says in the press release. "When you feel a mosquito bite, you swat it. With the vaccine, there is redness and likely an itch so you can recognize that you have been bitten and can pull the tick off quickly, before it has the ability to transmit B. burgdorferi."
None of the vaccinated guinea pigs contracted Lyme disease after scientists removed the ticks once inflammation began; in comparison, around half of the unvaccinated guinea pigs developed Lyme disease at that point, the press release says. This test was an important because a human would realize there was a tick and remove it once they started exhibiting symptoms.
Furthermore, if the ticks were left to fall off on their own, they let go of vaccinated guinea pigs within 48 hours, and they consumed less blood from them. On the flip side, 80 percent of the ticks on the unvaccinated group held on for more than 96 hours, allowing more time for B. burgdorferi to slip into the bloodstream, reports Live Science.
"We showed that by altering the ability of a tick to take a blood meal, you can prevent an animal from being infected with the Lyme disease agent," Fikrig tells Gizmodo.
The vaccine will go through further animal trials, such as testing in rabbits, before moving on to human trials if the results continue to show promise, writes lead author Andaleeb Sajid, a disease research at the National Institutes of Health, for the Conversation.
"The mRNA vaccine saved us from COVID for sure," Jorge Benach, a microbiologist at Stony Brook University who co-discovered B. burgdorferi, tells Meredith Wadman for Science. "Now [Fikrig] is using stunning technology … with more than one antigen simultaneously. … I think it will be very, very useful for future vaccines."