A vaccine to fight Lyme disease, decades in the making, has received a temporary green light from the U.S. Department of Agriculture. But it’s not for people — it’s for mice.

The vaccine isn’t a rodent-sized injection, which wouldn’t work for targeting large populations quickly. Instead, it’s coated onto edible, nutrition-free pellets that mice gobble up.

The vaccine makes mice develop antibodies that neutralize Borrelia burgdorferi, the bacterium that causes most U.S. cases of Lyme disease. When ticks imbibe the blood of a vaccinated mouse, the idea goes, they won’t get an active infection and so can’t transmit the bacteria to people or other animals.
“Mice are probably one of the most important reservoir hosts for Lyme disease,” especially in the Eastern United States where Lyme disease is rampant, says Jean Tsao, a disease ecologist at Michigan State University in East Lansing who was not involved in developing the new vaccine. Reservoir hosts are animals with B. burgdorferi in their blood (SN: 2/5/21).

The vaccine has a conditional license, granted on May 9. That means it is available on request by groups such as federal and state health agencies under certain conditions for roughly one year, with the possibility of renewal.

The first well-documented case of Lyme disease in a person in the United States was in 1970. A vaccine for humans was available from 1998 to 2002, but it was taken off the market due to low consumer demand, likely related to fears over the vaccine’s safety. Some vaccinated people reported developing arthritis, but the U.S. Food and Drug Administration found no meaningful difference in joint problems in vaccinated versus control groups.

Both the mouse and human vaccines use a protein called OspA, found on the surface of B. burgdorferi, to spur antibody production and prevent infection.

Biologist Maria Gomes-Solecki co-led the early development of the new mouse vaccine. Her team distributed an early version of the vaccine to areas in upstate New York from 2007 to 2011. B. burgdorferi has a two-year life cycle in ticks. This and other factors mean it takes time to see meaningful reductions in infections, says Gomes-Solecki, of the University of Tennessee Health Science Center in Memphis. After two and five years of vaccination, the researchers found that tick infections were reduced by 23 and 76 percent, respectively, compared with control sites.

That early vaccine used live Escherichia coli bacteria to deliver the OspA protein. But the current, green-lighted version of the vaccine uses inactive E. coli. A 2020 study of the new vaccine found a 30 percent reduction in the proportion of infected ticks in residential areas after two years, compared with control sites. Several coauthors on that study work for US Biologic, the company Gomes-Solecki cofounded to develop the vaccine.
“The vaccine they have works, but it’s not spectacular” in terms of the rate of reducing B. burgdorferi–infected ticks, says Sam Telford III, an epidemiologist at Tufts University in Medford, Mass., who was involved in the development of the human vaccine and led research in the 1990s for vaccinating mice.

Edible vaccines targeted at hosts have worked well for other diseases and species. For instance, vaccinating prairie dogs against the plague has decreased levels of the disease. For now, it remains to be seen whether vaccinating mice will result in lower Lyme risks for humans. “With additional studies as the product rolls out … we’ll see more data on how well it does,” Telford says. “It’s certainly a step in the right direction.”

Researchers are studying many approaches to controlling Lyme disease, including genetically engineered mice that produce B. burgdorferi antibodies without the need for vaccination (SN: 8/9/17). Tsao and Telford are studying how to limit tick populations by controlling deer numbers. And a new vaccine for humans is in late-phase testing in several thousand people.

Vaccines that target wildlife hosts will remain one tool among many for managing exposure to Lyme disease, the researchers say. Showering after being in areas with ticks, wearing long sleeves and pants and doing tick checks will still be important.

“We have to continue to be vigilant,” Gomes-Solecki says.