As the US speeds up the search for a COVID-19 vaccine, tensions have erupted between government scientists and Moderna Inc, Reuters reported.

The federal government is supporting the Moderna Inc vaccine project with nearly half a billion dollars.

But the company has sparred 'with government scientists over the process, delayed delivering trial protocols, and resisted experts’ advice on how to run the study', according to sources familiar with the vaccine project. 

The sources said those tensions have led to a delay of more than two weeks in launching the trial of Moderna’s vaccine candidate, now expected in late July.

Some disagreements raise concerns about the relative inexperience of the young biotech company and what the sources described as its lack of staff and expertise to oversee the most critical phase of human trials. The US government does not face similar problems with recognized drug manufacturers such as AstraZeneca Plc and Johnson & amp.

Moderna and other vaccine developers are working with the US National Institutes of Health (NIH) and the Food and Drug Administration (FDA), as well as immunologist networks and other vaccine experts tasked by the NIH to help oversee trial design.

Moderna denied any mistakes on its part but admitted "differences of opinion” with experts involved in the effort to deliver on the Trump administration’s pledge to find a vaccine within months. It usually takes about ten years to develop a vaccine. According to Moderna, it has an experienced team that includes people who have run multiple large-scale trials.

"It has not been smooth or easy,” said Moderna spokesman Ray Jordan. "No one has ever done anything like this before — not Moderna, not the NIH, and not any of the other companies.”

In one disagreement, for example, Moderna executives resisted experts’ insistence on close monitoring of trial participants who might contract COVID-19 for changes in oxygen levels that could signal dangerous complications. According to Jordan, Moderna preferred to defer all decisions about monitoring to patients’ physicians but that the company ultimately agreed to some monitoring.

Despite the complex process, according to government and company statements, Moderna leads the race for vaccines.