My mum is 63 with diabetes and hypertension. she got the oxford covid shot on the 28th feb. she had no reaction, no side effects. from the last 5 days she has developed a reddish rash on chest and stomach area, very itchy with no other symptoms. why?

Not sure what day (after the 28th) you are asking this, but it is now March 17,so if this started March 12, it would not be from the vaccine. It would be unlikely to be from the vaccine any time. However, without seeing a rash, we cannot tell what it is or what it is from. I would recommend your mom contact her doctor and have the rash examined, so that she can have proper diagnosis and treatment.

Agree with Dr. Ungerleider. We really don't have a way to answer that question. This lesion would require medical history, visualization and possible testing to be able to provide an accurate diagnosis and a treatment plan.