I had measles and rubella as a kid so I wonder if that gives immunity.
The journal article speculates that a 29% similarity between a surface protein of rubella and a surface protein of SARS-Covid19 might be the mechanism. So yes this might be looking good for you.
Hhmmm...I had German measles...maybe that makes me immune?
Rubella titre can and does wear off with time. I had rubella as a kid, titre was good when I was pregnant with the first baby. A little less than 3 years later, it was gone and I had to have a rubella shot as soon as the second baby was born to protect any other babies who might come along.
So don’t bet on that theory. Most elderly folks have also had the diseases yet ate the most vulnerable to covid today. Our bodies simply wear out.