Hey,

Bachelor of Medicine and Bachelor of Surgery (MBBS) is an undergraduate degree of about five years duration.  It's not mandatory that you need to do your further studies if you want to practice.

People do further post graduation to gain specialisation in the relevant medical field as MBBS only gives you general degree and not specialised degree.

If AIIMS vacancy mentions that only MBBS candidate can apply you are good to go but if it mentions or requires a post graduate degree sorry to say.

The eligibility will depend upon the post for which allocation is needed.

Hope that helps.

Thank you.