Moderna Inc is on track to deliver between 600 million and 1 billion doses of its Covid-19 vaccine in 2021, Chief Executive Stephane Bancel said on Thursday, January 7, Reuters reports (via Hindustan Times).

Bancel said Moderna had orders for 500 million doses of its vaccine and could comfortably make at least 600 million doses. He told a conference organised by Oddo BHF that the group was working to meet or even exceed a target for 1 billion doses, however.

Bancel said it was still not clear how long the antibodies generated by the vaccines would last, but added that it could potentially be a couple of years.

The U.S. biotech company, which stunned the world last year by coming up with a vaccine against the disease caused by the new coronavirus in just a few weeks, received approval for its shot from the European Commission on Wednesday.

Given vaccines development and pharmacovigilance usually requires years, the protection duration of COVID-19 shots is a lingering question for scientists and regulators.