I think we spoke about this, if I remember correctly, and the idea was not to mention vaccines in the form, but to check the vaccination status in the interview process and choose the participant that are actually allowed to cross borders...
Second possibility is maybe that participants are themselves responsible for this part of their journey: so either they are vaccinated or they themselves pay for all the PCR tests necessary.
We have a problem if in the moment of our trading the law will demand BOTH vaccination and PCR, like some countries are demanding.