Health officials across both Bailiwicks have confirmed that they will adhere to new advice from the Joint Committee on Vaccination and Immunisation (JCVI).
The JCVI advises that anyone under 40 without an underlying health condition should be offered an alternative to the Oxford/Astrazeneca vaccine so long as an alternative is available, and it will not cause delays to the vaccination rollout.
The precautionary move comes after evidence of an "extremely small risk" of people suffering from blood clots after having the jab.
According to the UK's medicines safety regulator says 242 clotting cases have been reported from 28.5 million doses of the vaccine - though this risk is slightly higher among younger age groups.
However, officials are emphasising that the number of such cases remains low.
In both Jersey and Guernsey, the AstraZeneca jab will still be offered to those who are due to receive it as a second dose, unless they have reported symptoms of blood clots following their first vaccination.
Jersey's government also confirmed that the change may impact on the delivery time for vaccinations for islanders under the age of 30, though the island remains on track to have all adults offered both doses of the vaccine by the end of July.
Public health in Guernsey is already in discussions with colleagues in Alderney and Sark about how alternative vaccines can be delivered to impacted age groups.