Fewer people are turning up for Covid-19 vaccinations in Tayside and Fife as the roll out reaches younger age groups.
Did Not Attends have been increasing in recent weeks, according to the two health boards, who say work commitments and out-of-date address details registered at GPs are the main factors.
In Tayside, around 240,000 (69%) eligible people have had a first dose and 147,000 (42%) have had a second.
In Fife, the figure is around 220,000 and 120,000 respectively.
Neither authority has released the percentages of missed appointments.
NHS Tayside say uptake levels in Tayside “remain extremely high” and above the Scottish average across all cohorts to date.
A spokesperson said: “As the vaccination programme moves down through the age cohorts we are seeing people unable to attend their appointments for a number of reasons including work commitments, no longer being at the address registered with their GP or people rescheduling their appointment for a later date.
“Invitation letters will be sent to the address you have registered with your GP practice so it’s really important that your surgery has the correct details for you.
“If you’ve recently moved, or think your details may be out of date with your surgery, please get in touch to update your address.
“The vaccination team continues to closely monitor attendance at appointments and is developing options for alternative ways to deliver clinics to ensure that as many people in Tayside are able to take up the offer of vaccination when it is offered.
“The vaccine is your best protection against coronavirus and we strongly recommend that everyone gets the vaccine when offered it.”
Those to receive the letter have been asked to call 0800 030 8013 to ensure their central record is up-to-date.
Guidance from Scotland’s chief medical officer on minimising vaccine wastage includes maintaining a “reserve list” of people to call at short notice.
The advice states these should be care home or front line health and social care staff or second doses and ideally from the same cohort.
NHS Fife director of Pharmacy and Medicines, Scott Garden, added: “Over recent weeks we have seen an increase in the proportion of people who have failed to attend their appointment for Covid-19 vaccination.
“While the rates of those who do not attend fluctuates from day-to-day, the vast majority of people in Fife who have been invited for vaccination have done so, with the percentage of people in Fife attending remaining better than the average across the rest of Scotland.
“Getting vaccinated against Covid-19 remains the best available defence against the virus and its effects, and it remains vital that everyone who receives an appointment presents to get their jab.”
Over three million people in Scotland have now had a first dose of a vaccine, making up two thirds of the eligible adult population.
The next cohort to be invited are people aged 18 to 39, who should receive a letter by the end of July, depending on vaccine supply.
Those aged 30 to 39 will be invited first, followed by 18 to 29 year olds.