By Drew Hinshaw

The European Union's drug regulator recommended the use of AstraZeneca PLC's Covid-19 vaccine in people 18 and older, clearing the way for a shot that EU officials have considered critical in turning the tide of the pandemic in the region.

But Friday's announcement, from the European Medicines Agency, came with a warning that the shot hasn't been tested enough in people over 55 to be certain the shot works in those age groups. And while it was welcome in a region grappling with high levels of infections, thousands of deaths a day and extensive lockdowns, it was tempered by the serious challenges AstraZeneca is encountering in producing the two-dose shot.

Moreover, some European officials have reservations over using the vaccine -- which AstraZeneca developed with the University of Oxford -- to inoculate people over 65. The shot would likely work in the elderly, the EMA said, but there was limited data available.

The result is that Friday's decision might only slightly accelerate a vaccine rollout that has so far been slow.

The EU has inoculated 2% of its collective population, compared with about 6% in the U.S. and more than 10% in the U.K. The EMA authorized the vaccine developed by Pfizer Inc. in December and that by Moderna Inc. earlier this month.

"With this third positive opinion, we have further expanded the arsenal of vaccines available," said Emer Cooke, EMA's executive director.

The EU bet big on AstraZeneca's shot, preordering 400 million doses -- more than any other vaccine and enough to inoculate nearly half of the region's 450 million people.

But a Belgian plant has reported lower-than-expected output.

The EU expected to receive at least 100 million doses -- and perhaps as many as 120 million -- by the end of March. In December, the company said it would deliver just 80 million. Last week, AstraZeneca officials told EU leaders the bloc would receive as few as 31 million doses -- enough to vaccinate about 15 million people.

The shortfall has set off a public fight between the EU and AstraZeneca, with the bloc threatening to block the exports of vaccines abroad.

Compounding problems, Oxford and AstraZeneca recruited relatively few elderly test subjects during clinical trials. The EMA wanted 7,500 people older than 65 or who had serious health conditions to partake in trials, but AstraZeneca and Oxford didn't meet that benchmark.

On Thursday, the German Health Ministry said it would recommend that only people 64 and younger receive the shot, saying there wasn't enough data on whether it worked in older demographics.

If other countries adopt the same approach, the shot might largely be used for younger adults in high-risk jobs, and will do little to slow the pace of deaths in people over 65, a demographic that accounts for about 90% of the more than 400,000 Covid-19-related deaths in the EU.

Within days, EU authorities are set to formally authorize the use of the shot. Distribution could begin days later, following administrative procedures needed to coordinate a rollout across 27 member states.

Write to Drew Hinshaw at drew.hinshaw@wsj.com

(END) Dow Jones Newswires

01-29-21 1113ET