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. 2022 May 23;13(5):101972. doi: 10.1016/j.ttbdis.2022.101972

The epidemiology of infectious diseases in Europe in 2020 versus 2017–2019 and the rise of tick-borne encephalitis (1995–2020)

Victoria A Jenkins a,⁎, Guenter Silbernagl b, Lorraine R Baer c, Bernard Hoet a
PMCID: PMC9126000  PMID: 35662067

Abstract

Health control measures instituted in 2020 to mitigate the COVID-19 pandemic decreased the case numbers of many infectious diseases across Europe. One notable exception was tick-borne encephalitis (TBE). In Austria, Germany, Switzerland, Lithuania, and the Czech Republic, the upturn was significantly higher compared to the average of the three years previously (P<0.05), with increases of 88%, 48%, 51%, 28%, and 18%, respectively. Six countries reported TBE incidences of ≥5 cases/100,000, defined as highly endemic by the World Health Organization (WHO). Possible factors contributing to this surge may include increased participation in outdoor activities in endemic regions and increased tick counts/tick activity. In highly endemic regions, the WHO recommends that vaccination be offered to all age groups, including children.

Keywords: Tick, TBE, Climate change, COVID-19, Vaccine, Epidemiology

1. Introduction

The emergence in December 2019 of the new coronavirus SARS-CoV-2, the causative agent of COVID-19, quickly swept around the globe, and on 11th March 2020 the World Health Organization (WHO) declared the COVID-19 pandemic (WHO, 2020). Consequently, parts of Europe put in place public health policies to contain the spread of the virus. Recent reports from Switzerland (Steffen et al., 2020) and Germany (Ulrich et al., 2021) documented substantial reductions in almost all recorded infectious diseases in 2020 as compared to earlier years. In these countries, one of the only infectious diseases to see an increase during this period was tick-borne encephalitis (TBE) (Steffen et al., 2020; Ulrich et al., 2021). In this report, we used data from the health departments of various European countries to investigate the prevalence of select infectious diseases under surveillance during 2020, and further explored the trend in TBE cases from 1995 through 2020.

2. Materials and methods

Data were sourced from the websites of health departments of the countries listed in Table 1 . For the calculation of disease incidences per country, population denominator data were obtained from the Statistical Office of the EU (Eurostat) https://appsso.eurostat.ec.europa.eu (data extracted on 10 December 2021). The reported incidences for the year 2020 and the mean for the combined years 2017, 2018, and 2019 were compared using a chi-square test, with no adjustment made for multiple comparisons.

Table 1.

Source Data.

Country Data source Web Addresses
TBE Data 1995 - 2010 Süss 2011 Süss J., 2011. Tick-borne encephalitis 2010: epidemiology, risk areas, and virus strains in Europe and Asia-an overview. Ticks Tick. Borne. Dis. 2, 2–15.
TBE data ECDC Tick-borne encephalitis - Annual Epidemiological Report for 2019- 2014 https://www.ecdc.europa.eu/en/tick-borne-encephalitis/surveillance-and-disease-data/annual-epidemiological-report
Austria The Ministry of Health: Annual statistics of notifiable infectious diseases https://www.sozialministerium.at/Themen/Gesundheit/Uebertragbare-Krankheiten/Publikationen.html
Belgium Épidémiologie des maladies infectieuses https://epidemio.wiv-isp.be/ & https://wwwnc.cdc.gov/eid/article/27/8/21–1175_article
Czech Republic The State Institute of Public Health: Infectious Disease Information System http://www.szu.cz/publikace/data/infekce-v-cr
Denmark Statens Serum Institut: Annual reports on disease incidence https://en.ssi.dk/surveillance-and-preparedness/surveillance-in-denmark/annual-reports-on-disease-incidence
Estonia Health board: Incidence of infectious diseases https://www.terviseamet.ee/et/nakkus-haigused/tervishoiutootajale/nakkushaigustesse-haigestumine
Finland National Institute for Health and Welfare: Statistical database of the Communicable Diseases Register https://sampo.thl.fi/pivot/prod/fi/ttr/shp/fact_shp
France Santé publique france https://www.santepubliquefrance.fr/maladies-et-traumatismes/maladies-a-prevention-vaccinale/encephalite-a-tiques/le-scan/#tabs
Germany Robert Koch Institut: Infection epidemiological yearbook https://www.rki.de/DE/Content/Infekt/Jahrbuch/jahrbuch_node.html
Hungary State Public Health and Medical Officer Service: annual reports, data on infectious diseases https://www.antsz.hu/felso_menu/temaink/jarvany/Fertozo_betegsegek/Fertozo_eves_jelentesk & http://www.oek.hu/oek.web?to=2561&nid=1308&pid=1&lang=hun
Ireland Health Protection Surveillance centre https://www.hpsc.ie/a-z/vectorborne/tick-borneencephalitis/
Italy Epidemiology for public health: National arbovirus surveillance system: periodic bulletins https://www.epicentro.iss.it/arbovirosi/bollettini
Latvia Center for Disease Prevention and Control: Epidemiology bulletins https://www.spkc.gov.lv/lv/epidemiologijas-bileteni
Lithuania Institute of Hygiene: Summaries of annual health statistics reports https://www.hi.lt/sveikatos-statistika.html
Netherlands National Institute for Public Health and the Environment Ministry of Health, Welfare and Sport https://www.rivm.nl/en/news/spread-of-tick-borne-encephalitis-virus-in-netherlands
Norway National Institute of Public Health: Communicable Diseases Notification System (MSIS), NIPH https://statistikk.fhi.no/msis/sykdomshendelser?etter=diagnose&fordeltPaa=aar
Poland National Institute of Public Health: Department of epidemiology and surveillance of infectious diseases http://wwwold.pzh.gov.pl/oldpage/epimeld/index_a.html
Slovakia Public Health Office of the Slovak Republic: Epidemiological information system https://www.epis.sk/AktualnyVyskyt/PrenosneOchorenia/Grafy/Sezonalita.aspx
Slovenia National Institute of Public Health: Health Statistical Yearbook of Slovenia https://www.nijz.si/sl/nijz/revije/zdravstveni-statisticni-letopis-slovenije
Sweden The Public Health Authority (Fohm): Statistics on infectious diseases https://www.folkhalsomyndigheten.se/folkhalsorapportering-statistik/statistik-a-o/sjukdomsstatistik/?letter=ABC#listing
United Kingdom Gov.uk Tick-borne encephalitis: epidemiology, diagnosis and prevention https://www.gov.uk/guidance/tick-borne-encephalitis-epidemiology-diagnosis-and-prevention
Switzerland Federal Office of Public Health FOPH: BAG-Bulletin https://www.bag.admin.ch/bag/de/home/das-bag/publikationen/periodika/bag-bulletin.html
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Web links last accessed July 2021.

3. Results

3.1. Cases of TBE in select European countries (January 2020-December 2020)

The number of cases of TBE were found to have increased in 2020 compared to the average of the three years previously in thirteen select European countries: Austria, Germany, Switzerland, Finland, Norway, Lithuania, and the Czech Republic (Table 2 ) as well as in Slovakia, Slovenia, Belgium, Denmark, the United Kingdom and the Netherlands (Table 3 ). In five countries, the increases were significantly (P<0.05) higher — Austria (88%), Germany (48%), Switzerland (51%), Lithuania (28%) and the Czech Republic (18%). Significant (P<0.05) decreases in TBE were found in Poland (−36%) and Sweden (−27%).

Table 2.

Number of cases of notifiable infectious diseases in European countries (2017 – 2020).

infectious disease 2017 2018 2019 2020 Mean 2017 - 19 % change 2020 vs Mean P value 2017 2018 2019 2020 Mean  2017 - 19 % change 2020 vs Mean P value 2017 2018 2019 2020 Mean  2017 - 19 % change 2020 vs Mean P value
AUSTRIA GERMANY SWITZERLAND
Influenza 95,943 274,242 193,879 194,731 188,021 4 <0.0001 9098 13,986 13,768 11,347 12,284 −8 <0.0001
Pertussis 1411 2202 2233 665 1949 −66 <0.0001 16,834 12,907 10,302 7084 13,348 −47 <0.0001
Haemophilus influenzae 39 49 64 28 51 −45 0.0086 811 851 954 468 872 −46 <0.0001 113 138 124 80 125 −36 0.0012
Meningococcal disease 20 30 24 8 25 −68 0.0028 283 295 256 138 278 −50 <0.0001 55 63 44 20 54 −63 <0.0001
Streptococcus pneumoniae 545 611 615 356 590 −40 <0.0001 945 966 873 558 928 −40 <0.0001
Tuberculosis 570 480 474 402 508 −21 0.0003 5486 5429 4791 4194 5235 −20 <0.0001 534 509 431 366 491 −26 <0.0001
Norovirus 1173 1572 1900 868 1548 −44 <0.0001 73,273 77,583 78,665 43,627 76,507 −43 <0.0001
Rotavirus 203 181 184 203 189 7 0.5348 38,251 23,603 36,874 7852 32,909 −76 <0.0001
Hepatitis A 242 80 76 37 133 −72 <0.0001 1232 1043 873 1011 1049 −4 0.3615 113 104 78 72 98 −27 0.0368
HIV 3144 2818 3093 2206 3018 −27 <0.0001 466 407 430 283 434 −35 <0.0001
Gonorrhea 2559 2936 3941 3501 3145 11 0.0002
Chlamydia 11,100 11,147 12,410 11,298 11,552 −2 0.0057
TBE (tick-borne encephalitis) 123 171 106 250 133 88 <0.0001 485 583 445 748 504 48 <0.0001 269 375 262 457 302 51 <0.0001
FINLAND NORWAY SWEDEN
infectious disease 2017 2018 2019 2020 Mean 2017 - 19 % change 2020 vs Mean P value 2017 2018 2019 2020 Mean  2017 - 19 % change 2020 vs Mean P value 2017 2018 2019 2020 Mean  2017 - 19 % change
2020 vs Mean P value
Influenza 13,260 35,823 19,825 10,190 22,969 −56 <0.0001 10,851 20,855 13,253 6797 14,986 −55 <0.0001
Pertussis 402 481 557 288 480 −40 <0.0001 2424 2476 2536 812 2479 −67 <0.0001 805 739 782 270 775 −65 <0.0001
Haemophilus influenzae 73 89 77 41 80 −49 0.0004 120 91 98 38 103 −63 <0.0001 229 201 259 92 230 −60 <0.0001
Meningococcal disease 16 16 16 5 16 −69 0.0161 18 26 16 5 20 −75 0.0024 49 56 66 28 57 −51 0.0012
Streptococcus pneumoniae 822 761 748 315 777 −59 <0.0001 560 581 599 295 580 −49 <0.0001 1367 1408 1345 650 1373 −53 <0.0001
Tuberculosis 10 15 12 5 12 −59 0.0885 261 208 165 177 211 −16 0.0643 533 504 491 355 509 −30 <0.0001
Norovirus 3874 2336 3392 865 3201 −73 <0.0001
Rotavirus 269 359 206 131 278 −53 <0.0001
Hepatitis A 29 28 18 12 25 −52 0.0319 50 32 37 15 40 −62 0.0006 110 123 90 57 108 −47 <0.0001
HIV 159 151 149 132 153 −14 0.2055 213 191 172 137 192 −29 0.0017
Gonorrhea 604 501 607 482 571 −16 0.0053 1399 1659 1704 1047 1587 −34 <0.0001 2531 2712 3244 2731 2829 −3 0.0478
Chlamydia 14,535 14,911 16,179 16,225 15,208 7 <0.0001 33,754 31,995 34,742 33,316 33,497 −1 0.0026
TBE (tick-borne encephalitis) 85 79 69 92 78 18 0.2906 16 26 35 41 26 60 0.0749 391 385 358 275 378 −27 <0.0001
ESTONIA LATVIA LITHUANIA
infectious disease 2017 2018 2019 2020 Mean 2017 - 19 % change 2020 vs Mean P value 2017 2018 2019 2020 Mean  2017 - 19 % change 2020 vs Mean P value 2017 2018 2019 2020 Mean  2017 - 19 % change 2020 vs Mean P value
Influenza 7408 14,300 11,668 4198 11,125 −62 <0.0001
Pertussis 56 69 135 44 87 −49 0.0002 95 159 720 342 325 5 0.3995 21 27 26 68 25 176 <0.0001
Haemophilus influenzae 53 75 69 36 66 −45 0.0027 2 4 4 1 3 −70 0.3242 8 14 3 1 8 −88 0.0201
Meningococcal disease 4 9 4 4 6 −29 0.5213 9 8 9 6 9 −31 0.4551 81 40 37 12 53 −77 <0.0001
Streptococcus pneumoniae 160 195 220 82 192 −57 <0.0001 75 76 83 69 78 −12 0.5119 76 65 66 44 69 −36 0.0203
Adenovirus .
Tuberculosis 144 120 147 100 137 −27 0.0144 896 779 779 7 818 −99 <0.0001
Norovirus 861 1457 1240 351 1186 −70 <0.0001
Rotavirus 586 543 558 146 562 −74 <0.0001 1643 1301 1432 256 1459 −82 <0.0001 3901 3474 2912 253 3429 −93 <0.0001
Hepatitis A 45 15 20 30 27 13 0.7067 75 67 37 21 60 −65 <0.0001 57 22 17 9 32 −72 0.0004
HIV 219 190 178 147 196 −25 0.0070 371 326 259 257 319 −19 0.0158 190 84 70 36 115 −69 <0.0001
Gonorrhea 58 49 81 23 63 −63 <0.0001 184 170 128 67 161 −58 <0.0001 70 72 56 32 66 −52 0.0007
Chlamydia 1139 983 1090 935 1071 −13 0.0016 1512 1306 1249 828 1356 −39 <0.0001 397 257 248 175 301 −42 <0.0001
TBE (tick-borne encephalitis) 87 85 83 70 85 −18 0.2151 214 169 250 210 211 0 0.9223 474 384 711 669 523 28 <0.0001
CZECH REPUBLIC HUNGARY POLAND
infectious disease 2017 2018 2019 2020 Mean  2017 - 19 % change 2020 vs Mean P value 2017 2018 2019 2020 Mean  2017 - 19 % change 2020 vs Mean P value 2017 2018 2019 2020 Mean  2017 - 19 % change  2020 vs Mean P value
Influenza 5043,491 5239,293 4790,033 3164,446 5024,272 −37 <0.0001
Pertussis 667 752 1347 696 922 −25 <0.0001 15 23 7 13 15 −13 0.7111 3061 1548 1629 743 2079 −64 <0.0001
Haemophilus influenzae 21 32 15 10 23 −56 0.0241 108 115 99 60 107 −44 0.0003
Meningococcal disease 68 52 51 24 57 −58 0.0002 41 43 51 33 45 −27 0.1783 225 200 193 99 206 −52 <0.0001
Streptococcus pneumoniae 270 341 297 200 303 −34 <0.0001 1192 1355 1541 545 1363 −60 <0.0001
Adenovirus
Tuberculosis 5787 5487 5321 5532
Norovirus 3501 5358 5636 1485 4832 −69 <0.0001
Rotavirus 5299 2949 3906 746 4051 −82 <0.0001 32,995 23,263 34,019 5962 30,092 −80 <0.0001
Hepatitis A 772 211 240 183 408 −55 <0.0001 367 182 104 28 218 −87 <0.0001 2590 1455 1067 109 1704 −94 <0.0001
HIV 223 229 238 151 230 −34 <0.0001 1462 1351 1763 934 1525 −39 <0.0001
Gonorrhea 1030 1249 1348 208 1209 −83 <0.0001 321 332 524 250 392 −36 <0.0001
Chlamydia 2261 2041 2343 1571 2215 −29 <0.0001 923 780 913 102 872 −88 <0.0001 258 308 421 168 329 −49 <0.0001
TBE (tick-borne encephalitis) 687 715 774 854 725 18 0.0018 16 32 18 18 22 −18 0.5330 283 197 265 158 248 −36 <0.0001
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* P-value derived from the comparison of reported incidences for 2020 vs the mean of years 2017, 2018 and 2019 using a chi-square test, with no adjustment made for multiple comparisons.

Table 3.

Number of tick-borne encephalitis cases in European countries (1995 – 2020).

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Mean  2017 - 2019 2020 incidence
Austria 109 128 99 62 41 60 54 60 82 54 100 84 45 86 79 63 103 49 100 81 79 95 123 171 106 250 133 2.81
Belgium* 2 0 3 1 0.03
Czech Republic 744 571 415 422 490 719 633 647 606 507 643 1029 546 631 816 589 861 573 625 410 355 565 687 715 774 854 725 7.99
Denmark* 1 4 3 1 1 4 8 4 ? 2 2 2 4 1 1 1 1 1 1 1 4 5 4 3 0.07
Estonia 175 177 404 387 185 272 215 90 237 182 164 171 140 90 179 201 250 178 114 83 116 81 87 85 83 68 85 5.12
Finland 5 8 19 16 12 42 33 38 16 29 16 18 20 23 25 38 43 39 38 47 68 61 85 79 69 92 78 1.67
Germany 226 114 211 148 115 133 225 239 278 274 431 547 238 285 313 260 422 195 420 265 223 348 485 583 445 748 504 0.90
Hungary 234 224 99 84 51 45 76 80 114 89 52 56 62 70 64 50 43 44 53 31 24 19 16 32 18 18 22 0.18
Ireland 1 0 0.00
Italy 6 8 8 11 5 15 19 6 14 23 22 14 4 34 32 21 26 34 42 22 14 53 24 39 24 21 29 0.04
Latvia 1341 716 874 1029 350 544 303 153 365 251 142 170 171 181 328 494 429 367 265 173 169 230 214 169 250 210 211 11.01
Lithuania 426 309 645 548 171 419 298 168 763 425 243 462 234 220 617 612 365 495 501 353 336 633 474 384 711 669 523 23.94
Luxembourg 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00
Netherlands* 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 1 2 2 5 2 0.03
Norway 1 1 1 0 2 1 2 3 3 13 9 10 11 14 7 6 13 9 12 16 26 35 41 26 0.76
Poland 267 257 201 208 101 170 210 126 339 262 177 317 233 202 351 294 221 189 227 195 149 283 283 197 265 158 248 0.42
Portugal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00
Slovakia 89 82 76 54 63 92 75 62 74 70 50 91 57 79 76 90 108 107 162 117 88 174 75 156 161 176 131 3.22
Slovenia 260 406 274 136 150 190 260 262 282 204 297 373 199 246 307 166 247 164 309 100 62 83 102 153 87 187 114 8.92
Sweden 68 44 76 64 53 133 128 105 105 174 138 163 185 224 210 174 284 287 209 178 268 238 391 385 358 275 378 2.66
United Kingdom* 1 1 0 0.00
Switzerland 60 62 123 68 112 91 107 53 116 138 206 259 113 127 118 90 175 95 205 113 121 206 269 375 263 457 302 5.31
* suspected autochthonous cases only
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3.2. Case numbers and incidence of TBE (1995–2020)

The year 2020 saw the highest ever number of TBE cases since 1995 for eight countries (Austria, Switzerland, Germany, Slovakia, Finland, Norway, Belgium, and the Netherlands) (Table 3). The highest notification rates of TBE in 2020 occurred in Lithuania, Latvia, Slovenia, and the Czech Republic, with incidences of 23.94, 11.01, 8.92, and 7.99 cases/100,000 population, respectively (Table 3 and Fig. 1 ). These four countries as well as Estonia (incidence of 5.12) and Switzerland (incidence of 5.31) reported incidences of ≥5 per 100,000/year. Incidences of TBE per country per 100,000 inhabitants in 2020 is shown in Fig. 1.

Fig. 1.

Fig 1

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TBE incidence per 100,000 inhabitants in 2020.

3.3. Trends in other infectious diseases in twelve European countries (2017 – 2020)

With few exceptions, the number of cases of a range of infectious diseases, including airborne diseases such as Haemophilus influenzae, Meningococcal disease, and Streptococcus pneumoniae, were significantly decreased in 2020 compared to the average of the three years previously (Table 2). The largest and most consistent decrease was seen in rotavirus, where seven (Germany, Finland, Estonia, Latvia, Lithuania, Hungary, and Poland) of eight countries reporting on rotavirus recorded reductions of 53–93%. Other than TBE, pertussis, influenza, gonorrhea, and chlamydia were the only other infectious diseases to have seen significant (P<0.05) increases in 2020 vs. the mean of the three previous years, and only in select countries. Influenza increased by 4% in Germany, gonorrhea by 11% in Switzerland, chlamydia by 7% in Finland, and pertussis by 176% in Lithuania.

4. Discussion

Over a 25-year period from 1995 to 2020, the number of cases of TBE across many European countries has trended upwards. Specifically comparing 2020 to the mean number of cases of 2017–2019, countries in the alpine regions demonstrated significant increases of 48–88% in TBE, with record number of cases reported in Switzerland and Germany. Other countries that saw a significant increase in TBE cases during this period were the Czech Republic (18%) and Lithuania (28%). In contrast, the changes in total TBE cases in other Northern and Eastern European countries were non-significant when compared to data from 2017-2019, with the exception of Sweden and Poland where a significant decrease in cases was reported.

Other notifiable diseases, including airborne diseases such as Haemophilus influenzae, Meningococcal disease, and Streptococcus pneumoniae, were decreased in 2020 in Europe and other countries (Steffen et al., 2020; Sullivan et al., 2020; Ulrich et al., 2021). The reduction in these infections may be linked to mitigation efforts (including social distancing, school closures, travel restrictions, and mask wearing, and an emphasis on hand washing) put in place to prevent the spread of COVID-19 (Steffen et al., 2020; Sullivan et al., 2020; Ulrich et al., 2021). Furthermore, day-care closures were likely responsible for the consistently large decline in rotavirus, as interactions between infants and young children were reduced. A potential explanation for the rise in pertussis in Lithuania could be increased health seeking behaviours and subsequent pertussis diagnosis.

TBE, an infectious disease of the central nervous system caused by the tick-borne encephalitis virus (TBEV), is endemic in Eastern, Central, and Northern Europe as well as in northern China, Japan, Mongolia, and the Russian Federation (World Health Organization, 2011). Transmission usually occurs via the bite of an infected tick. Infrequently, though, humans also can be infected by consuming unpasteurised dairy products (Brockmann et al., 2018; Kohlmaier et al., 2021).

Factors driving TBE incidence can be classified into three areas: (i) tick abundance, (ii) population at risk, and (iii) surveillance characteristics (Martin et al., 2020; Ocias et al., 2019; Ulrich et al., 2021; World Health Organization, 2011). Tick abundance is related to environmental conditions, including land use, weather, host reservoirs, and climate change, and can be very focal (Süss et al., 2008). An earlier occurrence of spring can accelerate tick development (Jaenson et al., 2012). Additionally, milder winters permit winter activity of ticks and may increase population of hosts to sustain greater tick populations (Süss et al., 2008). The weather conditions in Switzerland during winter months of late 2019/early 2020 were suitable to meet these conditions and may explain the high number of TBE cases in 2020. Indeed, the national average winter temperature rose to 0.7 °C (MeteoSchweiz, 2020). Unusually high winter temperatures, with a national average over 0 °C, have occurred only four times in Switzerland since 1864, when temperature record-keeping began (MeteoSchweiz, 2020). Complimenting this was the arrival of a very early spring 2020, as classified by the spring index (Federal Office of Meteorology and Climatology MeteoSwiss, 2021).

Changes in human behaviour (e.g., increase of at-risk outdoor recreational activities) can put people at greater risk of exposure to ticks and thus TBE. This is one factor that may have contributed to the increase of TBE during the COVID-19 lockdown, as shown by the actual versus predicted numbers in Austria and Germany. The predicted number of TBE cases for 2020 based on negative binomial regression models ranged from 142 to 156 for Austria (vs 250 actual), 663–670 for Germany (actual 748), and 465–472 for Switzerland (actual 457) (Rubel and Brugger, 2020, 2021). Interestingly, a 225% increase in visitor frequency to public green spaces, including national parks and public gardens, was reported in the Google Mobility Report of May 2020 for Germany (Schweizer et al., 2021).

Underreporting to surveillance systems in 2020 may have been a factor in some countries where there was a decrease in TBE. One analysis from Poland suggested that access to specialised diagnostic testing for TBE may have been limited during the pandemic due to overburdened healthcare resources (Sulik et al., 2021).

A limitation of this study is that mandatory reporting of infectious diseases varied across countries; as such, the data found on the websites of health departments were not uniformly available for all countries. In addition, changes in health care seeking behaviours and the number of laboratory tests conducted during the pandemic may have altered compared to the previous years, and these factors may have led to reporting bias for 2020 (Simões et al., 2020).

5. Conclusions

The overall trend in number of TBE cases across Europe is on an upward trajectory, although with regional and temporal variations. Several factors may be involved, including global warming and social behaviours. Long-lasting morbidity from TBE, limiting function and quality of life, are seen in up to 30% of those hospitalised with TBE (Bogovič et al., 2018; Kohlmaier et al., 2021). With no curative treatment available, vaccination remains the most effective method to prevent infection, with reported effectiveness rates of 95–99% (Heinz et al., 2013; Erber et al., 2022). The WHO recommends TBE vaccination for adults and children in highly endemic (≥5 cases/100,000 population/year) areas and targeted vaccination in specific geographical locations or when participating in at-risk outdoor activities (World Health Organization, 2011). Compliance with TBE vaccination is low in many European countries (Erber and Schmitt, 2018). Thus, increasing awareness and education regarding vaccination against TBE for those travelling to or residing in endemic areas are critical interventions for addressing this growing public health issue.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author statement

Victoria A Jenkins: Conceptualisation, Data extraction, Data analysis, Roles/Writing – original draft, Writing – review & editing.

Guenter Silbernagl: Data analysis, Writing – review & editing.

Lorraine R Baer: Roles/Writing – original draft, Writing – review and editing.

Bernard Hoet: Conceptualisation, Data analysis, Writing – review & editing.

Declaration of Competing Interest

Victoria A Jenkins, Guenter Silbernagl, and Bernard Hoet are employees of Bavarian Nordic. Lorraine R Baer is an employee of Baer PharMed Consulting, Ltd, which received funding from Bavarian Nordic for medical writing support.

Acknowledgements

Gerhard Dobler for discussions regarding epidemiological factors influencing variations in tick density.

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