I had the same issue - I had to recheck I had understood what 'person-years' means, and then run some tests on some simple population numbers to check that you could accurately determine the total population by multiplying by 12.

Could the confusion possibly be due to some of the recently vaccinated not having this status for a whole month but just 3 weeks? I don't think so, but nothing else comes to mind.

There is a lot of criticism of this report. When I get a free day, I will trawl through it and see if clarity can be achieved.