Well, yes, the mechanism that causes people with Down Syndrome to be susceptible to COVID is specific to COVID. But I understood the questioner to be asking ab

Well, yes, the mechanism that causes people with Down Syndrome to be susceptible to COVID is specific to COVID. But I understood the questioner to be asking about respiratory infections in general (including flu) since the linked article already addresses COVID susceptibility. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3074212/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3074212/