Novavax Inc has pushed back the timeline for reaching its production target of 150 million COVID-19 vaccine shots per month until the third quarter due to supply shortages including bags used to grow cells, a company spokeswoman told Reuters.

Novavax executives had previously said full-scale vaccine production could be achieved by mid-year. In January, the company told Reuters it expected to reach full production capacity by May or June.

“We said during our earnings call that we expect all capacity being online by around mid-year. We’re continuing to refine that timing as we get closer, which now leads us to think we’re online/at full capacity by Q3,” Novavax communications director Amy Speak said by email on Monday.

“There are some supply shortages that come and go that have contributed to the revision in timing,” she said, adding “these have included things like the bioreactor bags and filters.”

After releasing impressive UK trial data, Novavax could receive UK regulatory authorization for its vaccine as early as this month.

The Maryland-based company is one of many coronavirus vaccine makers that have had to push back production timelines due to industry wide shortages of raw materials and difficulties getting plants up and running.

Last month, Reuters reported that Novavax had delayed a planned deal to ship at least 100 million jabs of its 2-shot vaccine to the European Union, in part because of supply challenges.

In a Saturday interview with the Guardian, Novavax Chief Executive Stan Erck said the company has faced difficulties sourcing key production materials including single-use bags used to grow vaccine cells.

“Single-use bags are facing critical shortages and delays,” said Mark Womack, chief business officer of AGC Biologics, a contract manufacturer that is producing materials used in Novavax’s vaccine.

Data released in March from the UK trial showed the vaccine to be highly effective against the original strain of the novel COVID-19, with 90% overall efficacy against the virus, as well as 86% efficacy against the more contagious variant B.1.1.7 first discovered in Britain and now rampant in the United States and Europe.

The data also suggests the jab provides some protection against a highly concerning variant that emerged in South Africa, which some drugmakers have said may require a booster dose to address.