The vaccination rate for elderly is closer to 90% and the elderly are those hospitalized. So it is more like, 10% of elderly are unvaxed. 20% of people hospitalized are unvaxed elderly. Therefore the vaccine cuts hospitalization for elderly in half.

Source:

https://health-infobase.canada.ca/covid-19/vaccination-coverage/

https://www.princeedwardisland.ca/en/information/health-and-wellness/covid-19-testing-and-case-data

Age distribution of hospitalized cases1 (years)

60 to 79 46.6%
80 and over 34.1%

or around 80% elderly.

Vaccination rates (1,2,3,4 doses)

60 to 69 95.03% (4,600,009) 1.50% (72,748) 93.53% (4,527,261) 74.94% (3,627,473)
70 to 79 97.51% (3,056,385) 1.24% (38,810) 96.27% (3,017,575) 83.34% (2,612,158)
80 and older 98.67% (1,691,174) 1.62% (27,798) 97.05% (1,663,376) 84.84% (1,454,077)

So actually, it is closer to a 75% reduction in hospitalization of elderly. Since <5% of elderly are unvaxed and 20% of hospitalizations are elderly unvaxed.

Anyway, this phenomenon is known as Simpson's Paradox, and here's a video on it (specifically using vaccine stats as an example): https://www.youtube.com/watch?v=XVRfBhy5vGI