Pugh et al.
Effectiveness of two doses of tick-borne encephalitis (TBE) vaccine
J. Travel Med. 2022; in press. doi:10.1093/jtm/taab193
Since autumn 2021, a TBE vaccine (based on the European subtype, strain Neudörfl) has been licensed in the USA. The primary vaccination series consists of three injections for individuals aged ≥1 year. The doses are administered at day 0, 14 days to 3 months later (1–3 months for individuals aged 1–15 years) and 5–12 months after the second dose.
Travelers mostly ask for health advice shortly before they travel, and thus there would not be sufficient time to complete the primary vaccination series prior to travelling to TBE endemic areas.
Would two doses of TBE vaccine help to protect against TBE in the short term? This has been answered by a recently published analysis of TBE vaccination in Austria for the years 2018–2020.
The authors analyzed vaccine effectiveness when two vaccine doses were given on-schedule (the second dose did not exceed 12 months) and off-schedule (the second dose exceeded 12 months as compared to when three doses were applied.
Of the 477 hospitalized patients during 2018–2020, the vaccine history was known for 421 patients. 361 (85.8%) patients were not vaccinated, 12 (2.8%) had received two doses only (on- and off- schedule), among them, 2 (0.5%) received two doses on-schedule, and 44 (10.4%) patients had received ≥3 doses. The calculated vaccination effectiveness was in the range from 94.6%–97.4% for both two doses only and three doses vaccination categories.
In Austria, the TBE vaccine based on strain Neudörfl is by far the most used TBE vaccine, and thus the deduced conclusion of the authors was that this vaccine may be used in the USA according to its licensure using two doses for short-term protection of travelers to TBE endemic regions. For long-term protection, a third dose must be applied.
(It is worthwhile to mention here that the Robert Koch-Institut [Berlin] is of the opinion that two doses of TBE vaccine given independent of the trademark confer 98% protection up to one year; see Snapshot week 11/2022).