In this context, although it has been demonstrated that the lower viral clearance observed in children with acute upper respiratory tract infections and in adult/older SARS-CoV-2-infected individuals may be associated with homozygous–homozygous variants of the IFNλ3/4 gene [32], the impact of the IFNΛ3/4 gene polymorphism on COVID-19 vaccination, especially in the older adult population, is still poorly understood. The gene discussed is IFNL3; the disease is COVID-19.