Health boards in Wales are rolling out third vaccinations to priority groups as the booster campaign gathers pace.
Some including Betsi Cadwaladr and Cwm Taf Morgannwg gave their first jabs last week, with a health worker and a care home resident among the first recipients in the UK.
Vaccinations for 12 to 15-year-olds are also due to begin soon.
Children in that age group will be offered one dose of the Pfizer vaccine following chief medical officer advice.
The Welsh government has said it aims to get the doses done by the end of the autumn half term.
Wales' chief medical officer Frank Atherton told BBC Radio Wales speed was of the essence in getting jabs done.
"It's important we roll out these booster jabs as quickly as possible," he said.
"The health boards have all been getting ready for this and will be moving quickly on this.
"It's quite important, the booster dose, because the vaccines are still maintaining that gap between high levels of community transmission, which we see in Wales, and the harms people experience.
"The fact we have waning immunity - that some of the effectiveness of the first dose people have is reducing - makes it really important that people come and get their booster."
Ty Ross Care Home in Treorchy, Rhondda, which is in the Cwm Taf Morgannwg health board area, began giving booster jabs on Saturday.
Resident Anne Webb, 85, is believed to be the first care home resident in the UK to get a third dose.
By Monday morning the majority of the residents had been jabbed, care home manager Gail Dean said.
"It's been great. We've had 14 of our 18 residents vaccinated, so we've only got a couple left to do," she told BBC Wales.
"Five members of staff were done on the weekend too which is a good reaction from everybody. Everyone is happy to be doing this.
"We've had to recently start having visitors back inside the building which has been a big step forward for us. I think everybody is happy to be having the boosters now so it gives us more confidence when we're having people inside the home.
"There is always concerns about going into winter when you work in elderly care. Flu is bad enough on its own; knowing we have Covid to deal with too is an added element to that."
What is the priority order for vaccinations?
Health boards are vaccinating people in the same nine priority groups as for the original vaccine roll-out.
These were in groups numbered 1-9 and included everyone aged 50 and over, frontline health and care workers, unpaid carers and those aged 16-49 who were clinically vulnerable or in an at-risk group.
At the moment everyone else under 50 is not receiving boosters.
The graphic shows the priority list when vaccines were first given from the end of last year.
What are the arrangements in my health board area?
Betsi Cadwaladr University Health Board, which covers north Wales, has begun vaccinations already.
It is vaccinating people in the same priority order as the original vaccinations, as long as there has been at least six months since the second shot.
It will begin vaccinating 12 to 15-year-olds from 4 October. Children will receive invitations to attend an appointment through the post at home.
There are not currently plans to vaccinate in school settings.
Cwm Taf Morgannwg Health Board, which covers part of south Wales, has already begun vaccinating people at care homes using mobile vaccination teams.
After that, everyone in priority groups 1-9 will be invited to attend appointments at community vaccination centres from 27 September, including people who originally had jabs done at their GPs.
Appointments for teenagers will be sent home and they will also start receiving vaccinations at centres from next Monday.
Powys Teaching Health Board started vaccinating on Saturday and is inviting everyone in groups 1-9 eligible for the booster as soon as possible after six months has elapsed since their second dose.
It will start vaccinating 12 to 15-year-olds from 4 October in mass vaccination centres and expects to issue its final invitations by the end of October.
Swansea Bay University Health Board started vaccinating health and social care workers at the end of last week and will give doses to over-80s and care home residents from Monday before moving down the priority groups who have received a second dose six months or more ago.
Jabs for 12 to 15-year-olds will begin on 4 October, who will be invited by letter to a mass vaccination centre in Swansea and Neath Port Talbot with the aim of contacting everyone by 1 November.
Cardiff and Vale University Health Board will begin vaccinating care home residents from Monday using a mobile vaccination team, and frontline health and care staff will be invited to attend a mass vaccination centre in the order they received their first and second doses.
Over-80s will be able to attend a GP-led centre or community pharmacy close to home to get their boosters. Other priority groups will be asked to attend a mass vaccination centre.
The board said vaccination of 12 to 15-year-olds with underlying health conditions or immunosuppressed had already begun. All others in that age group will be invited to mass vaccination centres by letter and jabs should start in early October.
Hywel Dda University Health Board in west Wales said people were being invited to come for boosters based on the chronological order they received their second doses, which should mean following the original priority groups in the main.
Jabs will be carried out at mass vaccination centres.
Those aged 12-15 will be contacted directly by the health board and invited to come to a mass vaccination centre as well. The health board is not publishing start dates.
Aneurin Bevan University Health Board in south-east Wales began vaccinating care home residents and carers on Monday and will start on healthcare workers from 27 September.
All other priority groups will be called in the same order as they were for their second dose six months or more ago.
Vaccination of 12 to15-year-olds with underlying health conditions has begun, while all others will be called by letter to attend, with the aim of offering an appointment to everyone by 1 November.