'non-immune' is formed in English by the prefix 'non-' (from Latin 'non', meaning 'not') attached to 'immune' (from Latin 'immunis'), where 'in-' meant 'not' and 'munus' meant 'service' or 'duty'.

'immune' comes from Latin 'immunis' (exempt from public service), passed into Old French and then Middle English as 'immune', and the modern English compound 'non-immune' arose by combining the productive negative prefix 'non-' with 'immune'.

Initially 'immunis' meant 'exempt from public service or obligation'; over time 'immune' shifted to the sense of being 'protected or exempt from disease or harm', and 'non-immune' therefore means 'not protected (against disease)'.