LISBON, Portugal — Portugal is joining other European countries in extending the use of AstraZeneca’s COVID-19 vaccine to people age 65 and over, after initial uncertainty about its effectiveness in that age group.

The General Directorate for Health also announced Wednesday that people with Down syndrome will be added to the Phase 1 priority groups due to their risk of developing serious COVID-19 symptoms.

Teachers, school auxiliary staff and social workers who deal with children are also moving to the front of the queue as authorities prepare to start easing a lockdown that began in January and brought school closures.

Health officials were due later Wednesday to unveil the country’s first mobile vaccination units, part of a drive to accelerate inoculations. Portugal, a country of 10.3 million people, has so far administered just over 1 million vaccine jabs.