Coronavirus disease 2019 (COVID-19) which is caused by the virus SARS-CoV-2 has resulted in an ongoing global pandemic. It is unclear whether the relatively low number of reported cases of COVID-19 in people with CF (pwCF) is due to enhanced infection prevention practices or whether pwCF have protective genetic/immune factors. This study aims to prospectively assess the proportion of pwCF, including both adults and children with CF who have evidence of SARS-CoV-2 antibodies over a two-year period. This study will also examine whether pwCF who have antibodies for SARS-CoV-2 have a different clinical presentation and what impact this has on their CF disease. The proposed study will recruit pwCF from paediatric and adult CF centres in Europe. Serological testing to detect antibodies will be performed on blood samples taken at month 0, 6, 12, 18 and 24 with additional time-points if bloodwork is available via normal clinical care. Clinical data on, lung function, CF-related medical history, pulmonary exacerbations, antibiotic use, and microbiology and vaccination receipt, will be collected during routine clinical assessments. Associations will be examined between socio-demographic and clinical variables and serologic testing. The effects of SARS-CoV-2 infection on clinical outcomes and analyse end-points will be examined to explore any age-related or gender-based differences, as well as subgroup analysis of outcomes in lung-transplant recipients and pwCF receiving CFTR modulator therapies. As pwCF receive COVID-19 vaccination a comparison of the development and progression of anti-SARS-CoV-2 antibodies in pwCF following natural infection and vaccination SARS-CoV-2 over time will be performed.