A group of researchers led by Michael Diamond of Washington University School of Medicine in St. Louis have developed a vaccine that is effective in mice against Powassan virus, an emerging tick-borne virus that can cause life-threatening encephalitis in humans. They also show that the vaccine produces antibodies that protect the mice against other, related tick-transmitted flaviviruses. These findings appear in the journal  Cell Reports.

Worldwide, tick-borne diseases afflict hundreds of thousands of people every year, with many of those cases occurring in the USA. The most common tick-borne disease in the USA, by far, is Lyme disease, which is caused by an infection with Borrelia burgdorferi, a spirochete bacterium.

The number of other tick-borne diseases are rapidly expanding. Among these are other bacterial diseases, such as anaplasmosis and Rocky Mountain spotted fever, as well as diseases caused by protozoan and viruses, including babesiosis and Powassan virus encephalitis.

Vaccines prevent diseases from measles to rabies

Understandably, considerable attention is focused on accurate diagnosis and effective treatment of these infections. Prevention of exposure to these infections has received far less attention from the scientific and funding communities. Preventing tick-borne diseases is a challenge. Over the last century, vaccines for infectious diseases have prevented millions of illnesses and deaths from diseases ranging from measles to rabies.

But there is not a single human vaccine on the market for even one tick-borne disease in the USA. Even if there were a vaccine for, say, Lyme disease, people living in Lyme disease-endemic areas would need to remain vigilant about exposures to ticks because of the abundance of other tick-borne infections.

To counter this problem, some researchers are trying to develop anti-tick vaccines, though such a product is likely to be from years of comprehensive testing and commercial release.

Powassan virus is still rare, but it can be deadly and as with many emerging diseases, there was no known prevention or treatment for it. This vaccine is based on vaccine that is used to develop a vaccine for Zika: mRNA from the virus in question, encapsulated in lipid nanoparticles (LNP), produces subviral particles that share many features of the virus and provoke an immune reaction that produces protective antibodies.

Modified mRNA produces vaccine against flavivirus vaccine against flaviviruses

In mice, the new vaccine was effective after one dose against two different strains of Powassan virus and against the more distantly related Langat virus. This work suggests that the LNP-encapsulated modified mRNA vaccine platform could be used to produce vaccine candidates for other flaviviruses by substituting in mRNA from the virus the researchers want to target.

"We are excited that this mRNA-based vaccine against Powassan virus was highly immunogenic and conferred protection against multiple members of the family. We plan to continue studying the molecular basis for its broadly neutralizing antibody activity and test the vaccine against additionally related viruses,"  he says.

Diamond and his colleagues hope that this could be a way to rapidly produce potential vaccines for new flaviviruses as they emerge and before they become epidemics.