France, Poland and Sweden on Tuesday issued recommendations not to use the COVID-19 vaccine developed by AstraZeneca for the elderly.
They join Germany and Italy which issued such recommendations last week.
Authorities in France and Sweden say the vaccine should be prioritised for people under the age of 65, both citing insufficient clinical trial data for older people.
"This recommendation will be re-examined in the light of the availability of additional data," France's national authority for health (HAS) said.
Sweden's public health agency said it expects such data "to come later in the spring from an ongoing and large US clinical trial in phase 3."
"It will include sufficient number of older participants to be able to draw more certain conclusions regarding the protective effect," it added.
Poland's government has set a lower threshold, recommending the use of the vaccine in people under the age of 60.
Germany was the first European country to issue such a recommendation, with the country's vaccine committee (STIKO) recommending the jab for people aged 18 to 64 last Thursday. It was followed by Italy on Saturday, which set the bar even lower at 55.
Euronews has contacted AstraZeneca for comment.
The Europea Medicines Agency (EMA) authorised the use of the AstraZeneca/Oxford University vaccine on January 29, noting that most of the participants in the studies it based its recommendation on were between 18 and 55 years old.
"There are not yet enough results in older participants (over 55 years old) to provide a figure for how well the vaccine will work in this group. However, protection is expected, given that an immune response is seen in this age group and based on experience with other vaccines; as there is reliable information on safety from this population, EMA's scientific experts considered that the vaccine can be used in older adults," it said.
Preliminary phase 3 clinical trial data released on Wednesday by AstraZeneca found that the vaccine is 76 per cent effective at preventing COVID-19 after a single dose, rising to 82 per cent following a second dose administered 12 weeks or more after the first.
Analysis of the data also showed that the vaccine reduced asymptomatic transmisison of the virus.
"This primary analysis reconfirms that our vaccine prevents severe disease and eeps people out f hospital. In addition, extending the dosing interval not only boost the vaccine's efficacy, but also enables more people to be vaccinated upfront," Sir Mene Pangalos, AstraZeneca's Executive Vice President of BioPharmaceuticals R&D, said in a statement.
"Together with the new findings on reduced transmission, we believe the vaccine will have a real impact on the pandemic," he added.