Regulators in the United Kingdom have approved full marketing authorization for Gaithersburg-based Novavax’s updated, protein-based COVID-19 booster shot, but regulators in the European Union have delayed a decision.

The European Medicines Agency was expected to approve the Novavax booster last week, but it has requested more information. The agency reportedly had questions on the potency of the latest version, and wants to ensure consistency in the vaccine’s production across different production sites, the Financial Times reported, citing sources.

Novavax said in a statement it has responded to additional questions from the European Medicines Agency Committee for Medicinal Products for Human Use, and is currently awaiting feedback.

The updated Novavax COVID vaccine received approval from the U.S. Food and Drug Administration and Centers for Disease Control and Prevention last month. The vaccine has already shipped to U.S. pharmacies and health care providers. Novavax said it is too soon to evaluate U.S. vaccination rates, but it remains confident in the ongoing rollout in the U.S.

In addition to the U.S. and U.K., the updated Novavax COVID booster has also received full authorization in Singapore.