[katieHaylor (OP)]

Ian says:

When I turned up for my Covid-19 vaccination the only medical questions I was asked were any allergies and am I taking blood thinners? I take rivaroxaban. Why was the blood thinner information needed?

[evan_au]

When taking blood samples from a vein in your elbow, you are more likely to bleed and/or bruise if you are taking blood thinners.

However, a vaccination is into an arm muscle, and does not aim for a blood vessel, so this should be less of a problem.
- I guess there is a chance that they could hit a large blood vessel by accident, but this would be buried in muscle, and less likely to produce a visible bleed or bruise (compared to a blood sample from your elbow)?