Background Diversity in response to exposition to severe acute respiratory syndrome MESHD coronavirus 2 (SARS-CoV-2) is common and may be related to the innate immune response. The mucin MUC5B is an important component of the innate immune response and expression levels are associated with the MUC5B promoter polymorphism, rs35705950. The high expressing T-allele of rs35705950 is an accepted risk allele for a non-infectious aging lung disease MESHD called idiopathic pulmonary fibrosis MESHD pulmonary fibrosis HP (IPF). However, given the theory of trade-offs in aging lung disease MESHD and the importance of high expression for an adequate immune response, we hypothesize that the T-allele is protective against severe coronavirus disease MESHD 2019 (COVID-19). Methods We collected demographics, radiology, survival data and MUC5B rs35705950 allele status for 108 patients requiring hospitalisation for COVID-19 at St Antonius Hospital in The Netherlands. For comparison of allele frequencies and allele carriership with a white control cohort, the patient cohort was divided in a white (n=83) and non-white cohort. Results The patients had a median age TRANS of 66 years and consisted predominantly of males TRANS (74%) and 23 patients (21%) died. The T-allele frequencies of rs35705950 in white patients was 0.04 which was significantly lower than the T-allele frequency of 0.10 in white controls (p= 0.02). Moreover, comparison of the number of carriers TRANS and non- carriers TRANS of the T allele showed that only 8.4% of patients carried the T-allele versus 18% of controls (p=0.029; OR= 0.41, CI=0.19-0.94). Conclusions The MUC5B rs35705950 promoter polymorphism associates with COVID-19. The risk allele (T) for IPF is protective against the development of severe COVID-19 disease MESHD. This is a further example of a trade-off between optimal expression levels in the respiratory system which associates with aging diseases MESHD. However, these results require further investigation.