The Welsh Government has defended the speed of the Wales's Covid-19 vaccine rollout and said figures detailing the numbers vaccinated so far should be treated as "provisional".
Public Health Wales published data on Thursday showing that 35,335 people had received their first dose of the Pfizer/BioNTech vaccine by December 27.
Figures released by the UK Government show 786,000 people had received the vaccine by that date, with 31,016 in Northern Ireland and 92,188 in Scotland.
The Welsh Conservatives criticised the Welsh Government for "lagging behind the rest of the UK" and called for ministers to "step up".
In a written statement, health minister Vaughan Gething said the Welsh NHS had done an "admirable job" given the vaccine's characteristics created logistical challenges.
Mr Gething said: "Comparisons are naturally being made on the number of vaccinations administered by the four nations of the UK. The latest data has been published today.
"Whilst I recognise the data indicates there are other nations ahead of us, the national data presented at this very early stage of the vaccination rollout should be considered provisional and a snapshot of ongoing activity.
"We know, for example, that there will be lags in data entry.
"There are likely to be small differences between nations and figures for each country may be disproportionately impacted by any delivery or data issues within countries."
Mr Gething said other "local factors" were expected to have contributed to the figures, including a Covid-19 outbreak linked to a vaccination centre in Cardiff that meant it was unable to operate for two days.
He insisted that daily vaccination rates were increasing across Wales, with health boards preparing for "significant expansion in capacity" due to the rollout of the Oxford/AstraZeneca vaccine.
Some GP surgeries will be administering the Oxford jab from Monday.
The number of vaccination centres has increased from 14 to 22 and more staff are being deployed over the coming weeks - with some areas doubling capacity.
Mr Gething said "great care" had also been taken to minimise waste of the Pfizer/BioNTech vaccine despite its "very challenging" storage and distribution requirements.
Fewer than 1% of doses have been unable to be used, which he described as "testament to the efforts of pharmacy and nursing professionals" at vaccination centres in Wales.
Andrew RT Davies, shadow health minister for the Welsh Conservatives, praised NHS staff for doing an "incredible job" to administer the vaccine.
But he said "confusion" had been seen since the first vaccine was given in Wales in December, with many people aged over 80 "desperately waiting" for their appointment.
"Sadly, Wales is still lagging behind the rest of the UK, with Northern Ireland delivering nearly as many vaccines as Wales, putting Wales at the bottom of the percentage of population league table," Mr Davies said.
"There are three million people in Wales, the Welsh Government needs to step up and take some leadership in ensuring that the vaccine gets out quicker."
Mr Davies said Wales should be administering 100,000 vaccines per week, which he described as "a target we're a long way off".
In his written statement, Mr Gething said he would follow the advice of the four UK chief medical officers to prioritise first doses of the vaccine.
Second dose appointments given from Friday will be within 12 weeks from the first dose, to allow capacity to be "reappointed" to first doses, following the "latest scientific advice".
Mr Gething said the Joint Committee for Vaccination and Immunisation (JCVI) had advised that priority should be given to administering the first dose to as many at-risk groups as possible, rather than providing two doses in a short time.
"It will ensure that more at-risk people are able to get protection from a vaccine in the coming weeks and months, reducing deaths and starting to ease pressure on our NHS," he said.
On Thursday, Rhun ap Iorwerth, shadow health minister for Plaid Cymru, wrote to Mr Gething calling for publication of the evidence to justify the delay between the two doses of the Pfizer/BioNTech vaccine from 21 days to 12 weeks.
Mr ap Iorwerth said the "sudden switch" represented a "very significant departure" from previous guidelines.