It could be possible that [some, (0,100]%, portion of the benefit provided by] the vaccines wear off after a certain amount of time. This makes statistics like 99.7% of Waterford have been vaccinated perhaps less insightful than something like 34% (or whatever the actual number is) have been vaccinated in the last 6 months.
edit: added [some portion, (0,100]%, of the benefit provided by]
edit: added [some portion, (0,100]%, of the benefit provided by]