An immunisation campaign is being launched in Scotland following a rise in the number of children contracting a potentially fatal disease.
Most children have been vaccinated against the disease
The chief medical officer wants 200,000 Scottish children between the ages of six months and four years to have booster jabs against haemophilus infleunza type B (Hib).
A similar catch-up campaign is also targeting young children south of the border.
Dr Mac Armstrong said babies were offered the vaccination at about two, three and four months of age.
"Uptake is high - over 96% - but over the last few years there has been a small but significant increase in the number of cases of Hib disease," said the chief medical officer.
"It is important that we take action to arrest this increase in new infections before it becomes a more serious concern, and that is why this one-off booster is being offered.
"Appointment invitations, together with detailed information leaflets, have been issued to parents of younger children who will be vaccinated first and this process will continue over the summer.
"The aim is to ensure that all children who are between six months of age and their fourth birthday receive a Hib booster vaccination by late summer."
Hib causes a number of serious diseases, including meningitis and septicaemia.
Before 1992, when children in the UK started to be vaccinated against the disease, between 60 and 80 cases were reported each year in Scotland.
That had fallen to just four cases by 2000, although the numbers rose to 13 the following year and 29 in 2002.
The UK Joint Committee on Vaccination and Immunisation (JCVI) recommended the booster campaign, which is also being undertaken in England and Wales.
Posters, factsheets and information leaflets are also being distributed to raise awareness.