People in their thirties will receive the Pfizer vaccine for their first dose, following advice they should not be given AstraZeneca where possible.
The new guidance has come from the Joint Committee on Vaccination and Immunisation (JCVI), which says that alternatives should be found for the under 40s.
NHS Shetland has subsequently had a rethink how it will deliver vaccines to the younger age group.
It says anyone in this group who has already received AstraZeneca will receive the same vaccine for their second dose.
The JCVI advice changed after a review on extremely rare blood clot-related side effects.
But NHS Shetland has stressed this does not mean AstraZeneca can not be used in this age group – only that an alternative is preferred.
The JCVI had already changed the guidelines for the 18-30 age group.
Interim director of public health Dr Susan Laidlaw said the risk of clotting complications in those under 40 who received AstraZeneca was very low.
“The JCVI is clear that in the 30-39 group, any of the UK vaccines is better than no vaccine, unless there are specific medical contra-indications,” she said.
“There may be some circumstances where NHS Shetland may still offer AstraZeneca because it is the only one that is practical under specific circumstances.”
More than 14,500 first doses and 8,800 second doses have already been completed in Shetland with more than 650 people vaccinated at Gilbertson Park on Thursday.