Interferons are proteins made by the human body to fight off infections. These proteins protect our cells by 'interfering' with a virus's ability to replicate. In 2009, a gene called IFNL4 was discovered and shown to affect the outcome of infection with hepatitis C virus. The IFNL4 gene controls the expression of the IFNL4 protein. Many people do not make this protein because they carry an incomplete form of IFNL4. People who do not make this protein may be more or less susceptible to certain infections than those who do make it. We will use data from the UK Biobank to identify infectious diseases for which outcome depends on whether or not a person can make the IFNL4 protein. Additionally, we will explore whether the form of the IFNL4 gene a person carries affects their risk of dying.