Another option can be found in the comments to a Bionic Mosquito blog.
In response to Anonymous’ suggestion, there followed:
Jeff LeVesque April 12, 2021 at 7:22 PM
“…you can say that you are participating in the clinical trial but keep to yourself that you are the control group.”
I like this quite a bit, but I think it will be interesting to see what reactions I get when telling people I’m in the control group.
My version will go like this: As a member of the control group in the ongoing clinical trials, it is vitality important that I not get the shot.”
As always, so many thanks for all your efforts, Marie-Louise