This worked for my husband, too. We bought a special $60 hat on Amazon to make sure he was doing it right so we could avoid multiple physical therapy appointments and the associated bills; thankfully it worked very well. Once he had the movement down, we gave the hat to a doctor friend of ours to help spread the love.
DizzyFIX Vertigo Trainer for BPPV (Benign Paroxysmal Positional Vertigo) https://www.amazon.com/dp/B005GRG6PA/ref=cm_sw_r_cp_api_i_BDAZ7HQ5TXKYGGFX13BP
I've had some vertigo like a decade ago. They call it BPPV (Benign paroxysmal positional vertigo). One possible cause is debris inside the inner ear that confuses those tiny hairs that tell your brain what position your head is in. There is an exercise you can do at home to settle those tiny bits of debris. You can also go to a doctor and they will go through the exercise with you.
If you look up Benign paroxysmal positional vertigo on youtube, you will see a bunch of videos that run you through the head motions that will settle the debris. If you want to make it easy on yourself, there is a device that helps you position your head properly. It helped with me a lot, but not 100%.
amazon.com/gp/product/B005GRG6PA
Not 100% sure that this was related to covid or the shot, but it happened at the same time. Might have been a coincidence.
Make sure your IPD is correctly set. Make sure you have a beast of a machine. Check your steamvr frame graph for frame drops/late starts etc and tweak if you can or avoid that particular game/experience. Stick with teleport locomotion games/experiences only, but a bad performing game or experience will make you ill regardless.
You also might have a issue with vertigo in general. I have issues with that and its called BPPV. Try the half-summersalt or Epley maneuver to get the calcium crystals in your ear back to where they should be. I got a thing called the Dizzyfix from amazon that guided me through the Epley. I am at some point going to post my experiences with Vertigo and Motion sickness with the Vive and Rift to /r/vive into one big post.
Ginger may help(take it like 30 minutes in advance). I like pickled ginger(the stuff they give you with sushi), or those Gin-gins candies:
lying flat on the floor on a rug or carpet(no pillow) with a fan pointed right on me is the only thing that sooths me if I screwed up and went too long with VR