(Bloomberg) -- Moderna Inc. said its Covid-19 vaccine manufacturing partners outside the U.S. are “facing delays” due to laboratory testing issues that occurred in recent days.

While the problem has been resolved, it has slowed release of Moderna’s vaccine to markets outside the U.S., a company spokeswoman said in an email.

The problem will cause short-term adjustments to vaccine delivery outside the U.S., she said in the email.

Moderna is currently shipping vaccine as it makes it, which means it has no extra stock in storage to smooth over these types of temporary supply interruptions, spokeswoman Colleen Hussey said in an email.

Shares of Moderna fell as much as 4.5% in New York trading on Tuesday.

Earlier, South Korea’s prime minister said at a meeting that Moderna had notified the country that an adjustment in the vaccine supply schedule is “inevitable” due to a “production setback issue.”

“We will remain in close contact with governments, recognizing the importance of delivery planning for vaccination roll-out,” Moderna said in the statement. “Moderna and its manufacturing partners are working together to minimize this shortfall across all impacted nations.”

Moderna didn’t specify where the problems occurred. Its partners outside the U.S. include Lonza Group AG, which makes the vaccine substance, and Laboratorios Farmaceuticos Rovi SA in Spain, which fills vaccine vials.

(Updates with stock reaction in fifth paragraph)

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