The COVID-19 vaccine developed by drugmaker AstraZeneca has been approved as the third to be distributed in the European Union.
The European Medicines Agency said clinical trials showed it was "safe and effective at preventing COVID-19 in people from 18 years of age".
It added that the vaccine can be used in older adults aged over 55.
But some EU member states have indicated they will not use the vaccine in older people.
Lithuania's deputy health minister Zivile Simonaityte said trials for people older than 55 were not "comprehensive", while Germany's independent vaccine advisory committee recommended that the shot is only given to people below 65.
Meanwhile, French president Emmanuel Macron told the AFP news agency on Friday: "What I can tell you officially is that the first feedback we have today is not encouraging for those over 60-65 years old on AstraZeneca."
Neither France nor Germany officially decided to restrict the AstraZeneca vaccine.
Friday's announcement by the EMA follows the earlier approval of vaccines developed by Pfizer/BioNTech and Moderna.
Unlike the other two vaccines, AstraZeneca's jab does not need to be stored at low temperatures and is cheaper per unit.
The EMA's executive director Emer Cooke made the formal announcement at a press briefing on Friday afternoon.
“At least some protection is expected,” Bruno Sepodes, of the EMA’s expert committee, said at the briefing. He acknowledged that "the exact level of protection cannot be estimated for the time being.”
The agency noted there were not yet enough results to demonstrate how well the vaccine will work in older participants aged over 55.
But she said the decision to approve the vaccine for elderly people despite the small number of people tested in those age brackets was to make options available to EU member states.
"We are saying that according to the information we have and the scientific evaluation, it [the AstraZeneca vaccine] can be used in patients over 18, and we're not restricting it to under 55s," she said.
"And this is based on the evidence in the trials, the safety profile and the immunogenicity that chose an expectation of effect in older populations.
"It's about making sure that when countries are looking at [what] they need and what the profile of their population is, that they have this option available to them."
On Thursday Germany's vaccine committee said the AstraZeneca jab should only be given to people under 65 because of "insufficient data" over its efficacy.