Lyme disease: Final trial ends 20-year wait for a vaccine against the tick-borne disease How does the Lyme vaccine work? It targets an "outer surface protein" of the Lyme bacterium called OspA that’s present in the tick’s gut. It’s estimated a tick must feed on someone for about 36 hours before the bacteria spreads to its victim. That delay gives time for antibodies the tick ingests from a vaccinated person’s blood to attack the germs right at the source. In small, early-stage studies, Pfizer and Valneva reported no safety problems and a good immune response. The newest study will test if the vaccine, called VLA15, really protects and is safe. The companies aim to recruit at least 6,000 people in Lyme-prone areas including the northeast US plus Finland, Germany, the Netherlands, Poland, and Sweden.