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Tick-borne encephalitis vaccine scheme expands

Cases of TBE have fallen slightly, but in Kustavi on the west coast, the number has been growing steadily.

Ticks carrying TBE are spreading. Image: Yle
Yle News

The Finnish Institute for Health and Welfare (siirryt toiseen palveluun) (THL) will expand Finland's national vaccine programme against tick-borne encephalitis (TBE) in 2020 to include new regions where coverage is most needed.

Some islands in Lake Lohja in southern Finland will be added to the vaccination scheme, as well as the municipality of Kustavi in western Finland, where cases of the potentially deadly disease have risen for the past five years running.

Free TBE vaccines continue to be available in Åland, Parainen and Simo, southern Kemi, the Kotka archipelago, Sammonlahti in Lappeenranta and Preiskari island near Raahe.

Image: Paula Collin / Yle, Tanja Ylitalo / Yle

This vaccination measure only works against TBE – it does not prevent the contraction of Lyme disease and it does nothing to repel ticks themselves, despite unclear marketing of the service and imprecise branding as a "tick vaccine".

Anti-TBE vaccines have been part of Finland's national vaccine programme since THL instated the service in Åland in 2006. Other regions were added to the scheme in 2017 (Parainen, Simo), 2018 (Kemi, Lappeenranta, Kotka) and 2019 (Lohja).

THL: Cases in 20 percent of municipalities

THL reported 69 TBE cases last year. That was down from 79 cases in 2018 and 82 cases the year before that.

"Expanding the programme and developing local vaccine recommendations has probably helped to bring the number down," said THL researcher Sari Huusko.

Tracking statistics since 2015 show TBE disease incidence to be highest in the seaside town of Parainen, with 53 cases per 100,000 inhabitants. Last year, nine cases were reported there.

Other high-incidence regions included Simo (42/100K), Kustavi (30/100K) and Åland (28/100K).

There were no cases of tick-borne encephalitis reported at all in some 80 percent of Finland's municipalities between 2015 and 2019.

Theory: Watery hotspots

Tick expert Jani Sormunen from the University of Turku said he is not surprised that the THL opted to broaden the scope of its vaccine coverage.

Story continues after photo

Sormunen collecting specimens last autumn. Image: Minna Rosvall / Yle

"There are strong indications in Finland and the other Nordic countries that ticks have proliferated greatly during the past two decades. Incidence is expected to spread to more regions," Sormunen said.

As to why incidence is so much higher in certain places than the rest of the country, Sormunen said it is a mystery.

"Risk regions appear to follow bodies of water. A waterway may form a physical barrier for host mammals in the wild, preventing them from travelling or gathering in groups on the shore."

Image: Paula Collin / Yle, Tanja Ylitalo / Yle

Another theory is that large bodies of water even out extreme weather fluctuations, affecting the activity and survival of ticks in their larval stage, a crucial stage in the spread of the virus.

This exceptionally warm winter may raise tick populations in Southern Finland as mammals survive better, Sormunen said, but sufficient data is still needed to make predictions. There has been no winter this warm in the THL tick record, as tracking began in the 2010s.

"A few winters ago there were freezing temperatures but no snow. The frost went in deep and killed a lot of the arthropods in the earth, but it had no effect on the tick population at all. So it may be that this warm winter won't have an effect this summer either," Sormunen said.

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