LONDON, Aug 23 (Reuters) - Novo Nordisk has hired Thermo Fisher as its second contract manufacturer for its hugely popular weight-loss drug Wegovy, a source familiar with the matter told Reuters.

Thermo is doing the filling of the Wegovy injection pens at its factory in Greenville, North Caroline, the source said, declining to be named because the information is confidential.

Novo Chief Financial Officer Karsten Munk Knudsen told Reuters in May the company had signed up a second contract manufacturer in the United States, but the identity of the company has not previously been reported.

A Novo spokesperson declined to comment for this story.

The Danish drugmaker is scrambling to boost output of the drug to meet soaring demand in the United States and after production problems at the factory in Brussels, Belgium, operated by its first contract manufacturer, Catalent.

Wegovy launched in the United States in June 2021, the first-to-market in a new class of highly effective weight-loss drugs. It leads to an average weight loss of around 15%, alongside changes to diet and exercise.

In May, Knudsen said a third plant would start producing later this year and he hoped to add more sites. He did not identify the third partner.

Catalent's factory in Brussels that fills Wegovy pens has repeatedly breached U.S. sterile-safety rules in recent years and staff have failed to perform required quality checks, Reuters reported last month.

It is not clear how much the factories are producing. (Reporting by Maggie Fick; Editing by Josephine Mason and Mark Potter)