NHS Grampian bosses have vowed to have the issues affecting their flu jab programme resolved within the next 10 days.
Hundreds of vulnerable north-east people were turned away last week after travelling for flu jabs.
In addition, would-be patients have shared their frustrations over letters arriving too late for people to make appointments and a seemingly forever-engaged phone line.
Now, health bosses heading-up the delivery of the flu jabs have said that issues affecting the system should be resolved within the next 10 days.
They have also reassured those eligible that they will receive their vaccine.
Additional phone lines will be put in place from tomorrow, with extra staff being parachuted in to answer calls and emails.
This will help with appointment letters and flu helpline issues.
More than 40,000 people in the over-65s and at-risk categories in the region have already had their jab as part of the programme- with more than 1,500 being seen each day.
NHS Grampian deputy chief executive, Adam Coldwells said: “Work continued at pace over the weekend to resolve these issues and to deliver the vaccine.
“In the next ten days we expect to be ahead in terms of getting letters delivered and people should be receiving these in good time.
“Unfortunately it is likely in next few days some people may receive their letters either on the day or after their appointment.
“These people do not need to worry, they should call the helpline and we will book them back in.”
Their helpline has been inundated with calls from people who had yet to receive their appointment.
Mr Coldwells urged people to be patient with them as the programme is still in the early stages.
He added: “We need people to be patient with us. Everyone will receive their appointment letter in the next three to four weeks.
“Please do not call the helpline if you haven’t received your letter. We will get to you. If you do need to call the helpline if you could leave it until later in the week that would be very helpful.
“Please be reassured people who have missed their appointment will get another appointment.
“Anyone who has not received a letter, please don’t worry, the Flu programme runs for many weeks yet, the letters are sent out in batches not all at the same time.
“No one will miss out on their vaccine as a result of these issues – that’s very important to remember.”
Flu vaccine clinics are being held in schools during the October holidays, with further clinics being organised while will run into mid-December.
A spokesman for NHS Grampian said: “To help our teams answer your flu vaccine queries more quickly we are moving to a new telephone system.
“From 9am, Tuesday, October 20, you should call 0345 337 9899. This is charged as a local rate call.
“First and foremost, this number is for those who have received an appointment that they wish to rearrange.”