But who is currently eligible for a third jag and have they received it?
The booster rollout in Scotland began on September 20, with older people in care homes.
The following day, online booking opened for frontline health and social workers.
From the end of September, all adults over 70 and those over 16 who are most at risk from Covid – those previously advised to shield – were due to be contacted by letter or by their GP about their third dose appointment.
And everyone else eligible for a booster – all over-50s, unpaid carers, everyone over 16 with an underlying health condition and adults in the same household as anyone immunosuppressed – were due to be invited from October.
However, the Scottish Government has since acknowledged this has not happened, and the programme has not yet moved to the under-70s.
Those aged 60 to 69 and over-16s with underlying health conditions will begin to receive invitations from late October, a spokesperson said.
All remaining eligible groups are set to be able to book online from mid November.
When asked about delays to the booster programme, the Scottish Government pointed to advice from the Joint Committee on Vaccination and Immunisation (JCVI), which stipulates that boosters should be given at least six months after the second dose.
But there are at least 400,000 people eligible for a third jag who have not received it.
As of April 25, six months ago, 299,819 health and social care workers and 594,960 people aged over 70 had received a second dose, meaning a total of at least 894,779 people (plus anyone in the extreme high risk category who does not also fit into either of those groups) are now eligible for a booster.
Currently some 489,363 third doses have been administered, a shortfall of at least 405,416.
Figures published by Public Health Scotland show 31,992 of the third doses given were to immunosuppressed individuals.
Information is not yet broken down further by age or local area.