Table 1 Data sources applied by all participating countries

Collaborative institution

Statens Serum Institut

https://en.ssi.dk/

Finnish Institute for Health and Welfare

https://thl.fi/en/web/thlfi-en

The Directorate of Health https://www.landlaeknir.is/english/

Norwegian Institute of Public Health https://www.fhi.no/en/

The Public Health Agency of Sweden https://www.folkhalsomyndigheten.se/the-public-health-agency-of-sweden/

COVID-19 cases

The Danish Microbiology database https://miba.ssi.dk/service/english

The National Infectious Disease Registry https://thl.fi/en/web/infectious-diseases-and-vaccinations/surveillance-and-registers/finnish-national-infectious-diseases-register

The Registry of Communicable Diseases https://www.landlaeknir.is/tolfraedi-og-rannsoknir/gagnasofn/gagnasafn/item35278/Smitsjukdomaskra-(Register-of-Communicable-Diseases)

The Norwegian Surveillance System for Communicable Diseases (MSIS) https://www.fhi.no/en/hn/health-registries/msis/

The Swedish Surveillance System for Communicable Diseases (Sminet) https://www.folkhalsomyndigheten.se/the-public-health-agency-of-sweden/communicable-disease-control/surveillance-of-communicable-diseases/

Vaccination coverage

The Danish Vaccination Registry https://www.ssi.dk/vaccinationer/boernevaccination/vaccinationsdaekning-og-aarsraporter/det-danske-vaccinationsregister-ddv

The National Vaccination Registry https://thl.fi/en/web/infectious-diseases-and-vaccinations/surveillance-and-registers/finnish-national-vaccination-register-and-monitoring-of-the-vaccination-programme

The Vaccination Registry https://www.landlaeknir.is/tolfraedi-og-rannsoknir/gagnasofn/gagnasafn/item15627/Bolusetningaskra-(Vaccination-Register)

The Norwegian Immunisation Registry (SYSVAK) https://www.fhi.no/en/hn/health-registries/norwegian-immunisation-registry-sysvak/

The National Vaccination Register (NVR) https://www.folkhalsomyndigheten.se/the-public-health-agency-of-sweden/communicable-disease-control/vaccinations/vaccination-register-and-vaccination-coverage/variable-list-for-the-national-vaccination-register/

Population

Statistics Denmark https://www.dst.dk/en

The Population Registry, Statistics Finland https://www.stat.fi/en/statistics/vaerak

The National Statistical Institute of Iceland https://www.statice.is/statistics/population/inhabitants/

The National Population Register https://www.skatteetaten.no/en/person/national-registry/

Statistics Sweden (SCB) https://www.scb.se/en/finding-statistics/statistics-by-subject-area/population/population-composition/population-statistics/

Educational data

The Ministry of Health’s student register https://www.dst.dk/en/Statistik/dokumentation/documentationofstatistics/the-student-registre

The National Education Database https://www.ssb.no/a/english/mikrodata/datasamling/nudb/nudb_20130607-en.html