Scotland's biggest health board has apologised for its handling of this year's flu vaccination programme.
It emerged earlier in October that NHS Greater Glasgow and Clyde (NHSGGC) had been inviting the youngest age groups for their flu jabs first.
Others had received letters inviting them to an appointment after the date had passed.
The health board said it was "very sorry" for any stress and anxiety caused.
It has issued a statement assuring the public that all outstanding flu vaccination letters to the 65-plus age group would be sent out this week.
All appointments will be scheduled before the end of November, the health board said.
Senior members of NHSGGC team met local MPs and MSPs on Monday to hear more details about the concerns raised.
Jane Grant, chief executive of NHSGGC, said: "On behalf of the health board, I would like to sincerely apologise to all those people who have experienced issues with their flu vaccination appointments.
"We are very sorry for any distress and anxiety this has caused, especially among the more vulnerable members of our local communities."
Ms Grant said there had been a "number of challenges" with the delivery of this year's flu vaccination programme, caused by the increased number of eligible people and the need to maintain physical distancing when administering the jabs.
"For those who received their letter after their appointment date, we will ensure that you get an alternative appointment," she said.
"We understand that many people have struggled to get through to our appointment line and we are very sorry for that.
"We have now employed an additional 20 call handlers to manage enquiries so that more people can be supported in a more timely way. If members of the public do need to change their appointment, please contact us on 0800 707 6699 or via email at firstname.lastname@example.org"
Ms Grant add that the health board had put measures in place to avoid the mistakes being repeated.
The Scottish government has said that with Covid-19 circulating at the same time as the flu, it was "more important than ever" to get vaccinated this year.
In addition to over 65s, health workers, those with medical conditions, social care workers, families of shielders and over 55s are being offered the flu jab in 2020.
Although little is still known about how Covid will interact with influenza, data emerging from southern hemisphere countries that have already had their flu season is encouraging.
It suggests the combination of social distancing and improved hygiene has resulted in historical lows of other respiratory virus infections.
Scotland's deadliest flu epidemic in recent times was in 1989 when 2,400 people died in the seven days to Christmas Eve.
This figure is also greater than the 1,978 people who died in the second week of April this year, the worst week so far of the Covid pandemic in Scotland.