The nursery rhyme is not about the plague.
Many take "Ring a Ring o' Roses" for a coded account of the 1665 plague. Folklorists disagree: the reading only appears after the Second World War, and earlier commentators never mention it. The decisive words are also missing from the earliest versions, and the symptoms do not match.
Useful: For any interpretation, check when it first appeared – not just how good it sounds.
Source: en.wikipedia.org