Originally Posted by fransknorge

This is because antibodies are easily measurable. Every other components of the immune system (and yes you are correct, there are a lots) are much more work to measure. Scientific are all aware of this and if you read papers measuring antibodies level there is always a clear line about a limitation of that study not measuring T and B cells.
This is the same for other vaccines actually, when I looked at old paper showing vaccine responses (influenza) this often about antibodies only and highlighted as a limitations. There are plenty of research paper about T and B Cells (and others) but those are long research papers spreading over a fairly long research time, not something that can be done in a few months.