The subject of a sometimes acrimonious row between the EU and Britain, the AstraZeneca Covid-19 vaccine has also fuelled debate over its effectiveness among the elderly.
Although the European Medicines Agency recommended the vaccine for adults of all ages last week, several countries have advised against administering the jab to older people.
Germany has already said it will not advise over 65s to get it.
Italy's medicines agency on Saturday approved the vaccine for all adults but recommended alternatives for people aged over 55.
"It is clear that seniors will not be vaccinated with this vaccine," Michal Dworczyk, the Polish government official in charge of vaccinations, told reporters on Monday.
And France is set to be the next EU nation to announce its own recommendation on the AstraZeneca vaccine, which was shown in clinical trials to be 62 percent effective in preventing Covid-19.
The main problem centres around the lack of data among elderly trial participants.
Developers AstraZeneca and Oxford University have been transparent in disclosing that fewer than 10 percent of those it tested the vaccine on were 65 or older.
Just 450 participants were over 70.
This compares with more than 40 percent of participants in the Pfizer/BioNTech vaccine trials who were over 55.
- 'Misunderstanding' -
This doesn't mean that the AstraZeneca vaccine doesn't work well among the elderly, but rather that there is little data to prove it does.
"It is sad to see people misunderstanding the situation here," said Peter English, a consultant in communicable disease control.
"They are confusing an absence of evidence, with evidence of absence."
The EMA said there was insufficient data to know for certain how effective the AstraZeneca vaccine is in older individuals.
"However, protection is expected, given that an immune response is seen in this age group," it said.
It concluded that the vaccine "can be used in older adults," as is already the case in Britain, which was the first country to authorise its use.
Yet it has remained cautions, noting that "currently available clinical trial data do not allow an estimate of vaccine efficacy in subjects over 55 years of age."
- 'Demand management' -
The scientific debate over efficacy comes amid a political one over logistics.
The British-Swedish pharma giant said on Sunday it would increase its vaccine deliveries to the EU by 30 percent, backing down on an announcement a week earlier saying it could only deliver a quarter of the doses originally promised the bloc.
French President Emmanuel Macron waded into the row last week, citing reports that the vaccine was "quasi-ineffective" for people over 65.
"What I can tell you officially today is that the early results we have are not encouraging for 60 to 65-year-old people concerning AstraZeneca," he said.
In response, John Bell, one of the Oxford vaccine developers, told the BBC he expected Macron's comments were "a bit of demand management."
Disease specialist Eric Caumes pointed out on Monday that several countries including France are vaccinating people over 80 with the Pfizer/BioNTech vaccine.
"We don't know its efficacy in this age group," he told BFMTV.