Powassan virus is spread to people by the bite of an infected tick. Although still rare, the number of reported cases of people sick from Powassan virus has increased in recent years. Most cases in the United States occur in the northeast and Great Lakes regions from late spring through mid-fall when ticks are most active. There are no vaccines to prevent or medicines to treat Powassan virus disease. Reduce your risk of infection from Powassan virus by avoiding ticks.