Nicola Sturgeon has said the time Scots wait for a second dose of a covid vaccine could be reduced from eight weeks if medical experts back such a move.
It comes as vaccination rates in Scotland dropped to their lowest level in three months.
The Scottish and UK Governments both follow guidance on jabs from the Joint Committee on Vaccines and Immunisations (JCVI).
Under current rules, there is a recommendation that adults wait for two months for a second jab after receiving a first to maximise the drug's effectiveness against coronavirus.
Scottish Labour has previously called on the Scottish Government to reduce the waiting time from eight to four weeks to allow a faster roll-out of second doses.
Speaking at a virtual session of the Scottish Parliament, Anas Sarwar again repeated the call - and said several countries around the world were now waiting just four weeks between doses.
But such a move was branded "irresponsible" by the First Minister today, who insisted she would continue to follow guidance from the JCVI and not go against it.
Second jabs would only be sped up if the JCVI recommended it, she added.
"In the entire lifetime of this parliament, no devolved government has gone against the recommendation of the JCVI on vaccination," she said today.
She continued: "It would be unthinkable for me to go against the advice of the JCVI.
"The JCVI is, I understand, looking at this question. If it was to recommend reducing the dosage interval, there will be fewer people more happy to do that than me."
Responding to an earlier question from Tory leader Douglas Ross on the speed of the vaccination programme in Scotland, Sturgeon said: "There are two constraining factors on the pace of roll-outs. One that has always been there, and one that has kicked-in as we go to second doses.
"The first is the volume of supplies - they tend to ebb and flow, although they are healthy at the moment.
"The second, as we go into second does, is the clinically advised gap of eight weeks between the first and second dose. Frankly, we can't give you your second dose until eight weeks have passed.
"So if we did a certain number of first vaccinations eight weeks ago, that limits the number of vaccinations we can do today.
"We are vaccinating as quickly as possible within those constraints and any look at our vaccination rates, relative to England, would show we are achieving that same performance in that respect."
Ross said: “On the vaccine rollout, which has happened at a phenomenal pace across the whole of the United Kingdom and allowed us to safely ease restrictions at a faster pace, progress here in Scotland has now slowed. Today’s figures are the worst in three months."
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