FDA Approves Pfizer's Tick-borne Encephalitis Vaccine

Judy Stone, MD

August 17, 2021

The US Food and Drug Administration (FDA) has approved Pfizer's TicoVac vaccine for the treatment of tick-borne encephalitis (TBE). The vaccine is approved outside of United States, and more than 170 million doses have been administered since 1976. The World Health Organization (WHO) recommends vaccination for everyone in areas where the annual incidence of clinical disease is highly endemic, defined as more than five cases per 100,000 population, which is primarily the Baltic countries of Europe but includes some regions of Central and East Asia.

GlaxoSmithKline's Encepur is also approved outside the United States, as is a vaccine from China and two from Russia. The efficacy of all the vaccines is greater than 95%. Pfizer's protection is 98.7% to 100.0% after the three-dose course. With the new approval, American travellers will be able to get immunized before their departure instead of waiting until they are overseas to start the series.

TicoVac can cause injection-site pain, headache, myalgia, and fever, as is typical with many vaccines.

Tick-borne Encephalitis

TBE is caused by a flavivirus and is transmitted by the bite of an infected Ixodes scapularis, or deer tick. Like the Powassan virus, another flavivirus, infection can be transmitted in minutes through the tick's saliva, so early removal of the tick might not prevent illness. This is different than Lyme disease, where vigilance and early removal of the tick can prevent transmission.

Reservoirs for the virus include mice, voles, and shrews. Large mammals (deer, sheep, cattle, goats) also serve to support tick multiplication. In addition to tick bites, ingestion of unpasteurized milk from infected mammals can transmit TBE.

TBE symptoms can range from none to severe encephalitis (brain inflammation). One-quarter of infected people develop encephalitis. Most recover fully, but one-third of those infected can develop lifelong damage and paralysis or cognitive deficits. Death is rare, except in those infected with the Russian strain.

The first phase of a TBE infection is typical of viral infections, with nonspecific fever, headache, nausea, and myalgia. The next phase involves an asymptomatic interval of about a week (range, 1 to 33 days), followed by symptoms of a central nervous system infection.

There is no treatment for TBE, and no antivirals with proven benefit. However, a recent case report describes the successful treatment of TBE with favipiravir.

For now, if you are unvaccinated, prevention is the only viable option. If you plan to travel to an endemic region and anticipate participating in outdoor activities (such as hunting or hiking), wear permethrin-treated clothes, use an insecticide, and don't eat or drink unpasteurized dairy products.

Judy Stone, MD, is an infectious disease specialist and author of Resilience: One Family's Story of Hope and Triumph Over Evil and of Conducting Clinical Research, the essential guide to the topic. You can find her at drjudystone.com or on Twitter @drjudystone.

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