Thousands of children across Scotland are facing delays in receiving their flu vaccination at primary school.
Scottish health boards confirmed flu programmes have been disrupted with a number of sessions being rescheduled.
Priority is being given to at-risk and younger children, with P4-7 pupils facing the most disruption.
A UK-wide shortage of the nasal spray Fluenz Tetra has meant health boards are receiving fewer vaccines than needed.
How many children have been affected?
Programmes started in Scotland in October to vaccinate against flu, which typically circulates in December, January and February.
All Scottish primary schoolchildren are currently entitled to the vaccine, however some will see it pushed back.
It is difficult to tell how many children have been affected, but 12 out of 14 health boards in Scotland have reported delays so far.
The health boards are following advice from the Scottish government to prioritise younger children aged two to five as well as five to 18-year-olds who have underlying health conditions.
NHS Grampian estimated 163 schools had been affected by the delays, meaning approximately 27,000 pupils in the region could face disruption.
NHS Lothian, NHS Dumfries & Galloway and NHS Shetland all confirmed they had faced some disruption to their flu programmes.
NHS Highland said deliveries UK-wide were between two and four weeks behind schedule, meaning primary school vaccination sessions due to start on 11 and 18 November had been postponed.
Pupils in P3-7 from 28 schools in the NHS Borders region will also face similar delays of about two to four weeks, according to the health board.
NHS Fife and NHS Forth Valley both said the schedule for children in P4-7 had been delayed due to the shortages.
Some vaccine sessions at primary schools in Ayrshire and Arran due to begin on 18 November will be postponed, according to the health board.
NHS Greater Glasgow & Clyde also confirmed there were supply issues, again leading to a delay in the school flu roll-out.
There has been minor disruption to the flu programme in Orkney schools, however some P6-7 sessions may be rescheduled to December.
NHS Lanarkshire said it had not had to reschedule any school sessions, however a small number of pupils who miss their school vaccines will need to wait longer to see a GP.
This is because GP appointments are being prioritised for younger children or those with additional risks until supply levels of Fluenz are back to normal.
NHS Tayside has not been affected by the UK-wide shortage and confirmed their flu programme was being carried out as normal.
The adult flu programme has also not been affected.
Why has there been a delay in the roll-out of flu vaccines?
Public Health England (PHE) said the UK-wide delay would affect about a quarter of the overall vaccinations ordered.
PHE buys and orders vaccine stock for all the devolved nations, so delays had been expected in Scotland and Northern Ireland.
AstraZeneca, which supplies the vaccine to the NHS, said it needed "to repeat some tests before a portion of our [Fluenz Tetra] vaccine supply can be released and delivered".
Delay of the vaccine is related to "routine testing" by the manufacturer and "is not related to the safety or the efficacy of the vaccine," according to the Scottish government.
A government spokesman said: "Once the vaccine manufacturer has completed the testing, then it will be possible to determine the number of schools potentially affected and the likely timescale for the vaccine becoming available."
What advice is there for parents?
Parents and carers of those in high-risk groups are urged to make an appointment with their GP.
Health boards affected by the delays have ensured their flu programmes will be completed as soon as supplies are available.
Gregor Smith, deputy chief medical officer, said: "I would like to reassure parents and families that we are doing everything possible to minimise any disruption caused by the UK-wide delay in supply of Fluenz Tetra.
"We are working with Public Health England, Health Protection Scotland, NHS boards and other relevant partners to ensure that all eligible children get their flu vaccine as soon as possible.
"Those most at risk and children aged two to five-years-old will be prioritised initially, with boards working to ensure all other eligible children, such as those at primary school, receive their vaccine in due course."
Who gets the children's nasal spray flu vaccine in Scotland?
The flu vaccine is free and offered to:
- All children aged two to five (who are not yet in school) at their GP practice
- All primary children at school
- Children of all ages with a long-term health condition, from six months of age
Source: NHS Scotland
* NHS Western Isles could not be reached for a comment