The centres were built at very short notice by Powys Teaching Health Board’s estates team.
In Bronllys, Builth Wells and Newtown, they have converted empty spaces to quickly become clinical vaccination centres.
Each location had its own challenges; from upgrading electrics and installing IT infrastructure to building covered walkways, installing signage and flooring.
Carpenter Gareth Davies said: "Everywhere needed different things.
"In Builth Wells at the Showground we had to put up 30-40 banner signs just to help people find their way even before they get to the vaccine centre for traffic control.
"Then in some locations we had to install additional plumbing for new sinks.
"There were a team of about eight of us carrying this all out.”
The Newtown mass vaccination centre is the largest of the three in Powys.
With 12 lanes it can vaccinate huge numbers of people at a time.
The team took just six days to convert it from an empty shell to a fully operational vaccination centre.