Total COVID cases=5158+7737=12895. Ratio 7737:5158=60:40=3:2.
To compare the COVID cases for the two groups, it's necessary to adjust the figures so that they rest on the same base. One way to do this is to boost the figures to the common base of 100%. Then the breakthrough cases can be compared directly.
If 26% is equivalent to 5158 cases, then 100% is equivalent to (100/26)5158=19838.46 cases approx.
If 74% is equivalent to 7737 cases, then 100% is equivalent to (100/74)7737=10455.41 cases approx.
Now we can compare these two figures: 19838.46/10455.41=⅔×(74/26)=74/39=1.90 approx. This represents a ratio:
(over 50s):(under 50s)=19:10 approx.
This means that the over 50s are about 90% more likely than under 50s to get breakthrough infections.
In terms of shares we have 1.90/2.90=0.6549 approx, or over 50s have about 65.5% of the share of breakthrough infections.