Note. The Figure is an extension of the figure published Rohm et al. (2023). Saliva: collection of saliva via self-collection kit (Oragene kit, 2 ml); 1. strict lockdown and 2. strict lockdown: contact restrictions in private life, travel restrictions, closure of schools, gastronomy, retail, service sector, cultural institutions (e.g., museums, cinema, concerts) and social sports activities; lighter lockdown measures: contact restrictions in private life and closure of gastronomy, cultural institutions and social sports activities. Yellow boxes indicate additional data collections, that were not planned to be carried out at the beginning of TwinLife data collection in 2014.

* Interviews of the fourth F2F wave had to be substituted with CATI and CAWI interviews due to contact restrictions during the pandemic.