She said this means second doses may have to be prioritised at times in April.
Speaking ahead of First Minister’s Questions, Ms Sturgeon said she has had talks with representatives producing the Pfizer and AstraZeneca vaccines.
She said: “At present we expect that over the next month we will have approximately 500,000 fewer doses than we had previously anticipated.
“For that reason there may be periods in April where we need to prioritise second doses.
“However, I want to be clear today that we do still expect to offer a first dose of the vaccine to the remaining JCVI priority groups by the middle of next month as planned… we also still expect to have offered a first dose to all adults in the population by the end of July.”
Scotland has recorded seven deaths from coronavirus and 624 positive tests in the past 24 hours, Ms Sturgeon also told MSPs.
This brings the death toll under this measure – of people who first tested positive for the virus within the previous 28 days – to 7,536.
The daily test positivity rate is 2.7%, down from 3% on Wednesday.
There are 405 people in hospital confirmed to have the virus, down 17 in 24 hours, and 38 patients are in intensive care, no change on the previous day.
More than 2.2 million people have been given a first dose of the vaccine in Scotland – 2,230,002 as of 8.30am on Thursday, up 41,184 in 24 hours.
A total of 192,100 have had a second dose, up 10,221.