Outdoor recreation, tick borne encephalitis incidence and seasonality in Finland, Norway and Sweden during the COVID-19 pandemic (2020/2021)

ABSTRACT

During the pandemic outdoor activities were encouraged to mitigate transmission risk while providing safe spaces for social interactions. Human behaviour, which may favour or disfavour, contact rates between questing ticks and humans, is a key factor impacting tick-borne encephalitis (TBE) incidence.

We analyzed annual and weekly TBE cases in Finland, Norway and Sweden from 2010 to 2021 to assess trend, seasonality, and discuss changes in human tick exposure imposed by COVID-19. We compared the pre-pandemic incidence (2010–2019) with the pandemic incidence (2020–2021) by fitting a generalized linear model (GLM) to incidence data.

Pre-pandemic incidence was 1.0, 0.29 and 2.8 for Finland, Norway and Sweden, respectively, compared to incidence of 2.2, 1.0 and 3.9 during the pandemic years. However, there was an increasing trend for all countries across the whole study period. Therefore, we predicted the number of cases in 2020/2021 based on a model fitted to the annual cases in 2010–2019. The incidences during the pandemic were 1.3 times higher for Finland, 1.7 times higher for Norway and no difference for Sweden. When social restrictions were enforced to curb the spread of SARS-CoV-2 there were profound changes in outdoor recreational behavior. Future consideration of public health interventions that promote outdoor activities may increase exposure to vector-borne diseases.

KEYWORDS:

• TBE
• tick-borne encephalitis
• seasonality
• public health interventions
• COVID-19
• COVID-19 restrictions

Acknowledgments

We want to thank Sari Huusko for the initial idea about a paper on TBEV-incidence while she was employed in Finnish Institute for Health and Welfare. We also want to thank Erika Lindh for her support and expertise in the early stages of the manuscript. Thanks to Elizabeth Fleur Peacocke and Sharon Edmunds for proofreading the paper.

SJ and HV was funded by the Research Council of Norway and the project #TimeLyme (313286). HM and TD was partially funded by EU grant 874850 MOOD and is catalogued as MOOD 068. HM and TD would also like to acknowledge the funding from the Academy of Finland from the VECLIMIT project (decision No #329323). The contents of this publication are the sole responsibility of the authors and do not necessarily reflect the views of the European Commission.

Authors contributions:

Solveig Jore: Conceptualization, Investigation, Data curation, Resources, Writing – original draft and review & editing.

Hildegunn Viljugrein: Formal analysis, Methodology, Visualization, Writing – review & editing.

Marika Hjertqvist: Data curation, Resources, Writing – review & editing.

Timothée Dub: Writing – review & editing.

Henna Mäkelä: Data curation, Resources, Writing – review & editing.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Available on the public health institutes webpages

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/20008686.2023.2281055

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

The work was supported by the Academy of Finland [VECLIMIT project (decision No #329323)]; EEA Grants [874850 MOOD]; Academy of Finland [VECLIMIT project (decision No #329323)]; Research Council of Norway [project #TimeLyme (313286)].