A health board has launched a cancellation line for people unable to attend their Covid jab appointment after a small number of no-shows.
Cardiff and Vale University Health Board said the service would launch on Wednesday.
It comes after the board's Vale locality manager posted on social media they had 19 no-shows that day.
Meanwhile, Wales is sticking to a UK-wide policy of delaying a second Covid dose, the chief medical officer said.
Fiona Kinghorn, Cardiff and Vales' executive director for public health, said nearly 15,000 people had been vaccinated so far in the area.
She told BBC Radio Wales Breakfast it was "frustrating" that people had not arrived for their jab.
"It's frustrating but we need to investigate why that's the case," she said.
"And it's two-way thing - we need to do everything we can to make it easy for people, and people who've been invited need to do everything they can to turn up...
"If somebody's not well on the day and we've booked them ahead... we need to have a mechanism that they can tell us that they can't make it."
She said the number of no-shows was "very small in the scheme of things", adding: "The key messages is if we've booked you in, please do everything you can to turn up and let us know in advance if you can't."
The Welsh Government published its vaccine strategy on Monday, saying over 50s and those with underlying health conditions will be offered a jab by spring, and all other adults by autumn.
Invitations to attend vaccination appointments are generated automatically and people have been told to expect a letter, phone call, email or text from their health board.
Is Wales behind UK for second jabs?
At Wednesday's Welsh Government coronavirus press briefing, chief medical officer Frank Atherton said Wales was adhering to the UK-wide agreed policy on delaying second doses of Covid vaccine by up to 12 weeks.
Official data suggest fewer people are getting second jabs in Wales than in other UK nations.
More than 390,000 people in England have received a second jab while, in Wales, that figure is about 100, according to the UK government's statistics portal.
In Wales 101,371 first doses have now been given according to the latest figures, up from 70,000 on the weekend.
Dr Atherton said: "You will have to ask people in England why there are some cases where people have had second doses.
"By and large I am really pleased that everybody in Wales is understanding that a second dose given now is a first dose denied to somebody else and they need that protection."
Second doses had been given in some cases to avoid wasting vaccine after packs had been opened, though less than 1% of vaccine was being wasted in Wales, he said.
Dr Atherton said he would expect health boards to set up vaccination centres working around the clock if there were public demand for such a move.
It comes after Prime Minister Boris Johnson said he wanted to get vaccine centres in England working 24/7 "as soon as we can".
Is Covid here to stay?
Dr Atherton said it is too early to know whether annual coronavirus vaccines will be needed, but people will have to learn to live with the virus.
"It's pretty much a certainty that we are going to have to learn to live with coronavirus," he said.
"If that is the case then it's entirely likely that we may have to move to a situation, rather like flu vaccination, where we have to give a seasonal vaccine against coronavirus every year. But it is too early to know for sure."