NHS Greater Glasgow and Clyde has apologised after 200 Dumbarton and the Vale residents were turned away from pre-booked vaccine appointments.
The health board turned locals away from the Masonic Hall in Dumbarton on Wednesday night to prevent "unnecessary queuing".
Officials said there had been a power cut at the Church Street venue during the session but that staff had been able to continue working.
A spokesperson said: "We apologise to any patient who was turned away from our clinic to avoid queuing unnecessarily.
"Despite a power cut at the Masonic Hall, our staff were able carry on under emergency lighting, meaning 846 doses of the vaccine were given in total.
"If you have missed your appointment, please call the national helpline on 0800 030 8013 and you will be able to book a new one.
"We are doing everything in our power to ensure those with appointments, receive their vaccines as close to their original appointment time as possible."
It comes as Dumbarton and the Vale MSP Jackie Baillie said she had been contacted by several angry residents who were asked to go home without receiving their booster jag.
Ms Baillie - who raised the issue at First Minister's Questions in the Scottish Parliament on Thursday - called on the Scottish Government to make appointments more accessible in the fight to beat the virus.
READ MORE: What did Nicola Sturgeon announce today in Omicron update?
Asking the First Minister to investigate the situation, Ms Baillie said: "We can all accept that there will be glitches, but people in my constituency want to be vaccinated and they want to be vaccinated quickly."
In response to Ms Baillie's question in the Holyrood chamber, Nicola Sturgeon said: "For anyone who has an appointment and is unable to have that appointment fufufilled, they should phone the helpline as that is what is required. That is my advice.
The announcement of the new variant has significantly increased the numbers of people coming forward for their boosters.
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