A senior Chinese epidemiologist said the United States should be the priority in the next phase of investigations into the origin of Covid-19 after a study showed the disease could have been circulating there as early as December 2019, state media said.

The study, published this week by the US National Institutes for Health (NIH), showed that at least seven people in five US states were infected with SARS-CoV-2, the virus that causes Covid-19, weeks before the United States reported its first official cases, Reuters reports.

Zeng Guang, chief epidemiologist with the Chinese Centre for Disease Control and Prevention, told state-owned tabloid the Global Times that attention should shift to the United States, which was slow to test people in the early stages of the outbreak, and is also the home of many biological laboratories.

“All bio-weapons related subjects that the country has should be subject to scrutiny,” he was quoted as saying.