Seems to me that they are saying the vaccines may only be maximally effective for about 6 weeks, after which they start to become less effective over time at preventing hospitalizations.
Cathi got a link for that? I searched the text but could only come up with paywall results.
https://www.ed.ac.uk/files/atoms/files/scotland_firstvaccinedata_preprint.pdf
It is too early in the vaccine program to get definitive numbers on how long efficacy for serious disease (hospitalizations) will last. Estimates I have read from various sources indicate 4 to 8 months. But, early clinical studies have been disappointing.