I got my 2nd dose of moderna vaccine 4 days ago, my arm started to swell, was red and itchy on the 2nd day, today is the 4th day and it has subsided but only a little bit. can i take a shower even if my arm is still swollen, red and itchy?

I see no reason not to keep up your normal bathing routine after the vaccine. It does not interfere with its effectiveness or any side effects you may experience.

Agree with Dr Ferguson, as no real reason to avoid normal daily activities. Injection reactions are not uncommon, and yours seems a bit more persistent than the usual. Since it seems to be improving give it time. Contact your doctor if it appears to be worsening.