The halt is temporary — the Leiden plant is expected to start churning out the Covid vaccine again after a pause of a few months — and it is not clear whether it has had an impact on vaccine supplies yet, thanks to stockpiles.

But over the next several months, the interruption has the potential to reduce the supply of Johnson & Johnson’s Covid vaccine by a few hundred million doses, according to one of the people familiar with the decision. Other facilities have been hired to produce the vaccine but either aren’t up and running yet or haven’t received regulatory approval to send what they’re making to be bottled.

Inside Johnson & Johnson’s executive suites, the decision to suspend production at Leiden prompted concerns that it would impair the company’s ability to deliver on its vaccine commitments to the developing world.