The COVID-19 pandemic saw a massive investment into collaborative  research projects with a focus on producing data to support public  health decisions. We relay our direct experience of four projects funded  under the Horizon2020 programme, namely ReCoDID, ORCHESTRA, unCoVer and  SYNCHROS. The projects provide insight into the complexities of sharing  patient level data from observational cohorts. We focus on compliance  with the General Data Protection Regulation (GDPR) and ethics approvals  when sharing data across national borders. We discuss procedures for  data mapping; submission of new international codes to standards  organisation; federated approach; and centralised data curation.  Finally, we put forward recommendations for the development of  guidelines for the application of GDPR in case of major public health  threats; mandatory standards for data collection in funding frameworks;  training and capacity building for data owners; cataloguing of  international use of metadata standards; and dedicated funding for  identified critical areas.