(Reuters) – Novavax Inc said on Monday it has begun enrolling volunteers for the second phase of an ongoing clinical trial of its COVID-19 vaccine candidate, with interim data expected in the fourth quarter of 2020.

In the new phase, the age range has been expanded, with adults between 60 and 84 years accounting for nearly 50% of the trial’s population.

Early-stage data from a small clinical trial of the vaccine has shown it produced high levels of virus-fighting antibodies, and the company aims to begin larger studies to obtain regulatory approvals as early as December.

The vaccine candidate is one of nearly 30 being tested in human clinical trials globally and lags candidates from AstraZeneca, Pfizer and Moderna that are in late-stage studies.

The U.S. government in July awarded Novavax $1.6 billion to test and manufacture its vaccine in the United States, with the aim of delivering a 100 million doses by January.

Britain has also tied-up with the company to buy 60 million doses of its vaccine candidate, some of which will be made using Fujifilm Diosynth Biotechnologies facilities in Stockton-on-Tees, northern England.

The study is targeting enrollment of up to 1,500 healthy volunteers at up to 40 sites in the United States and Australia, Novavax said.

Last week, the drug developer began a mid-stage study of its COVID-19 vaccine in South Africa.

(Reporting by Ankur Banerjee and Vishwadha Chander in Bengaluru; Editing by Arun Koyyur)