A previous idea to include young people in the list of those to be vaccinated first "was abandoned", an EU source said, without giving a reason.
"All persons from six months old with underlying chronic conditions (e.g. chronic respiratory diseases; chronic cardiovascular diseases and persons with congenital or acquired immunodeficiency)," should be vaccinated first, the experts from the 27 EU nations said in a written statement.
Those with the most severe symptoms should be at the head of the queue, they added.
Pregnant women and "health care workers" were the other two categories prioritised by the European Union Health Security Committee and the Early Warning and Response authorities.
The experts, who thus backed proposals from the European Commission, stressed that "it is the responsibility and mandate of each (EU) member state to develop a vaccination strategy for influenza A(H1N1)", known as swine flu.
"The priority groups identified... are indicative and countries may wish to adapt the prioritisation in line with their epidemiology, health services provisions and resources," the experts agreed.
The approach may also need to be changed "as the pandemic progresses".
EU health experts had already declared that there is no point in pre-emptive school closures or delaying the start of the new term in order to tackle swine flu.