AstraZeneca is still waiting for the go-ahead from the US drug regulator to restart the clinical trial of its potential Covid-19 vaccine in the United States, Chief Executive Pascal Soriot said on Thursday.

“We are the sponsor of the US study. We then provided all this information to the FDA (US Federal Drug Administration) and we are waiting to hear their decision,” Soriot told a virtual World Economic Forum discussion.

The US trial of AstraZeneca’s Covid-19 vaccine candidate, initially developed by the University of Oxford, remains on hold while regulators investigate an illness in one of the participants, even after a British study and other programmes outside of the United States have resumed.

US Health and Human Services Secretary Alex Azar said on Wednesday the continued suspension showed the FDA took vaccine safety seriously.

A document posted online by Oxford university last week stated the illness in a British participant that triggered the pause on Sept. 6 may not have been associated with the vaccine.