The Prevalence of Asymptomatic Infections with Tick-Borne Encephalitis Virus and Attitude towards Tick-Borne Encephalitis Vaccine in the Endemic Area of Northeastern Poland

In Poland, tick-borne encephalitis (TBE) vaccination rate is low despite high incidence of severe infections with TBE virus (TBEV). However, infection with TBEV can be asymptomatic or mild, which makes the total number of cases difficult to assess. We aimed at assessing asymptomatic TBEV infections and describing attitudes towards the TBE vaccine. We studied 298 healthy adult blood donors and 180 children from the TBE endemic area of northeastern Poland for the presence of anti-TBEV IgG antibodies. We also surveyed a separate cohort of 444 adults. Thirty-eight blood donors (13%) and 38 survey respondents (9%) reported a history of a prior anti-TBEV vaccination. Forty respondents (9%) reported vaccinating their child in the past. Fourteen unvaccinated blood donors (5%) and four children (2%) were seropositive for specific anti-TBEV antibodies, suggesting a history of an undiagnosed TBEV infection. In the surveyed cohort, 130 (32%) expressed their intention to be vaccinated and 144 (36%) expressed their intention to vaccinate their child. This intention was significantly higher in respondents with a recent tick-bite, a diagnosis of tick-borne disease in a close relative, and in males. Our study shows that asymptomatic TBEV infections are common. The acceptance of TBE vaccine is low, but might be increased by communicating risks associated with tick bites.