Around 60,000 people in Scotland missed their vaccine appointment after invitations were not delivered in time.
First Minister Nicola Sturgeon said a “glitch” in the system had now been resolved – as she apologised to those who missed out.
She was questioned on what had gone wrong by Scottish Conservative Holyrood leader Ruth Davidson.
So far, more than 2.2 million Scots, almost half the country’s adult population, have received their first dose of the vaccine.
But Davidson said: “Last week, one in seven vaccine appointments were missed because of delays in delivering the letters.”
She added: “For those who received their letters too late it may have caused confusion, dismay and even distress.
“Of course there will be bumps in the road, but I cannot agree with the First Minister’s description of 60,000 missed appointments as ‘glitches’.
“Given the importance of the rollout, it is important to ensure there is no repeat.”
Speaking at Holyrood, the First Minister said the government was “aware of issues with the delivery of appointment letters in the early part of last week”.
Work is being done with Royal Mail and others to “understand all of the detail of that,” she added.
But Sturgeon stressed: “I have been given an assurance that the issue has been resolved.
“I want to apologise to anybody affected. There were around 60,000 appointments that were not attended.
“We are closely monitoring day-to-day uptake versus projections and trying to make sure we understand the reasons why people might not be attending for appointments.
“Undoubtedly last week that would have been partly down to the issue with letters, but there will also be other issues.”
Work to rebook appointments is already underway, the First Minister said, pledging this would be done “as quickly as possible”.