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FDA approved TicoVac, the first vaccine against tick-borne encephalitis for people ages 1 year or older who are visiting or living in areas endemic to the illness, late on Friday.

It has been a long road to U.S. approval for TicoVac, which the manufacturer noted has been approved outside the country since 1976 -- over 170 million doses have been administered since that time. TicoVac, also marketed in Europe under the name FSME-Immun, is an inactivated whole virus vaccine that mimics the tick-borne encephalitis found in nature, and induces neutralizing antibodies against the virus, Pfizer said.

Tick-borne encephalitis is a viral infection of the brain and spine, generally transmitted by ticks, but rarely from unpasteurized milk or milk products from infected animals. Symptoms resemble summer flu, but a third of people could develop long-term neurological effects, including cognitive changes, muscle weakness, or permanent paralysis. Up to 2% of people generally die from the illness.

Approval was based on that demonstrated seropositivity rates of 99.5% in individuals ages 1 to 15 years following three doses, and 98.7% to 100% in individuals ages 16 and older. The company also cited real-world data that found the vaccine to be 96% to 98.7% effective in people who received at least three doses.

The vaccine was well tolerated, with no unexpected adverse events or vaccine-related serious adverse events, Pfizer noted. In clinical studies, the most common adverse events in adults and children were local tenderness and local pain. Other adverse events included headache, fever, and fatigue.

The vaccine is administered as a , with different dosages for younger (ages 1 to 15 years; 0.25 mL) and older individuals (16 and up; 0.5 mL).

For the younger group, the first two doses are given 1 to 3 months apart, then a third dose at 5 to 12 months following the second shot. In the older group, the second shot can be given at 14 days to 3 months from the initial dose, with the third dose also at 5 to 12 months after the second. If ongoing exposure is expected, boosters can be given after 3 years.

Pfizer said TicoVac should not be given to anyone with a severe allergic reaction to any component of the vaccine. The company added that it may be less effective in individuals with altered immunocompetence. Because the vaccine contains albumin, there is an "extremely remote risk" of viral diseases and variant Creutzfeldt-Jakob disease, though no cases have been documented. Safety and effectiveness have not been established in pregnant women.

Currently, the European CDC recommends tick-borne encephalitis vaccine for people who live in or travel to endemic areas. Pfizer added that the CDC's Advisory Committee on Immunization Practices is slated to discuss recommendations for the vaccine at a future meeting.

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