Nicola Sturgeon announced last week that instead of the three to four weeks between doses of the Pfizer vaccine initially intended, the gap would be 12 weeks, following advice from the Joint Committee on Vaccination and Immunisation (JCVI).
The decision has faced some opposition, with relatives of those in care homes saying last week that the change would be confusing and distressing to older, vulnerable people.
The World Health Organisation warned against the strategy on Wednesday.
Alejandro Cravioto, chair of the WHO's Strategic Advisory Group of Experts on Immunisation (Sage), said the second dose should only be delayed in “exceptional circumstances”.
Doctors have also warned the turnaround has impacted NHS staff morale.
“Speaking to people across the country, it’s been a real kick in the teeth,” said Graeme Eunson, chair of the Consultant’s Committee at BMA Scotland.
“People consented to a treatment which has now been changed without any discussion.
Dr Eunson said the turnaround has been “incredibly poorly handled”.
"It’s just been unnecessary increased stress and anxiety for staff who are simply trying to do their best,” he said.
He added: “It is the final straw on top of this very heavily burdened camel, as staff have had to contend with a huge amount over the last nine months. This is not how you treat a workforce you value.
“If I consented a patient to treatment they would expect me to follow through on that treatment, and I don’t see why the same shouldn’t apply to all of us who consented to getting this vaccine.”
Willie Duffy, head of heath at Unison Scotland, said the union has been “inundated” with calls from healthcare staff concerned about the change.
“We’ve been inundated with people contacting us to raise their concerns about this [...] we’re not disputing the science, but staff took the first vaccination on the understanding that they required the second dose 21 days after the first, and now the government is saying that isn’t necessary,” he said.
“It’s had a real impact on staff.”
Michael Griffen, president of the Royal College of Surgeons of Edinburgh, said the college supported the decision, but not the handling of it.
“As a college we absolutely support it, but have been slightly disappointed by the messaging to make sure that people understand why that decision has been made,” he said.
“There are those who were waiting for their second dose, who have suddenly been told when they are not getting it, and they think well why not, they promised to give it to me.
“I can quite understand that confusion and anxiety.
“But without a doubt, that decision to give one dose to twice as many people is a good one, it’s the right thing to do and it’s in the interests of the general population.”
When asked earlier this week about the change to the dosing timetable, Nicola Sturgeon said: "The four chief medical officers have collectively given their advice to the four governments on dosing, and they have done that on the basis that the proposed approach allows us to vaccinate more people with a significant degree of immunity more quickly than under the original strategy.”