Some Edinburgh and Lothian vaccine centres had "literally no patients" for days amid an issue with missing appointment letters.
Edinburgh Live revealed last week that a number of people in the 60 to 64 age group hadn't received their letters when they were supposed to have done, raising concerns about the management of the vaccine booking system in NHS Lothian.
Several people told Edinburgh Live they only realised they were already booked in for their vaccination after calling the helpline.
Edinburgh Southern MSP Daniel Johnson told the Scottish Parliament that the issue had resulted in some vaccination centres having "literally no patients", with a number of people unaware of their appointments.
He said: "It became clear that there had been a major problem with the issuing of the blue letters, and that people between ages 60 to 65 in the Lothians had not been receiving their appointments.
"This resulted in the health board making pleas on social media for people to call and find out if they had an appointment."
He added that a source informed him that "some vaccination centres have had literally no patients over the last few days" and staff were asked to go out and "drum up support" to fill slots.
First Minister Nicola Sturgeon said on Tuesday that an investigation was being carried out in order to establish exactly how the problem came about, however she believes it may be a Royal Mail issue.
She added: "Let me give an assurance to everybody who is expecting or receiving their appointments that they will receive their vaccination, and if there is a need to rebook then that will be done through the system that is already in place."
The Scottish Government confirmed this week it had launched a probe into the issue, and had apologised to those affected.
A spokesperson said: “The Scottish Government is investigating with NHS National Services Scotland and Royal Mail to understand why there have been delays to appointment letters being received by people aged 60-64 in the NHS Lothian region.
"We would like to apologise to anyone who has missed their appointment as a result and for the inconvenience this may have caused them. We have been clear with the board that we expect anyone who has been affected by this issue to be rebooked swiftly.
“We are also working with the national vaccination helpline so that people within the NHS Lothian area can get through to speak to someone to help them get their vaccination, if they were affected by this delay.”
