The Portakabin building, which is already on site, is needed to help carry out the vaccination programme at Brewood Medical Practice, South Staffordshire Council’s planning committee heard on Tuesday.
The Kiddemore Green Road surgery is located in the Green Belt, where the temporary structure would be considered inappropriate development.
But committee members agreed that there were very special circumstances to allow it to remain in place.
The Portakabin building includes two consultation rooms, a waiting area with a small reception and a toilet.
A report to the planning committee said: "Permission was initially sought for a temporary period of five years, however this has been reduced to three years following discussion with the planning team.
"The applicants explain that following their relocation to this site demand for their services has increased and the medical centre is put to full use, meaning there is no space to expand.
"There are also three residential developments approved for the catchment area which is expected to result in a further uplift to patient numbers.
"The Portakabin building is intended to be used to aid the on-going flu and Covid vaccination programme while a long-term solution to the problem is explored and funding is sought.
"The effects of Covid requirements and the need for social distancing has compounded the surgery’s existing capacity issues.
"There are no other opportunities to expand the surgery’s capacity in the time-frame required and the facility needs to be situated immediately adjacent to the existing surgery.
"The proposal is temporary, of modest size/height and has been situated so that it is behind the existing building.
"Visually it causes no harm to the Green Belt, is reversible in nature and would support a critical NHS need."
Committee members unanimously agreed to grant temporary permission for the portable building on Tuesday.
Ward councillor Diane Holmes said: "I have no problem with this. It is sited in the Green Belt but it is temporary."
Committee member Councillor Penny Allen said: "We have to do everything possible to help our GPs in this current climate.
"I know from my own surgery it has been quite difficult and there is a mass vaccination programme for flu.
"They are making suitable arrangements for their patients."