Now the Strabane factory is back in operation making protective clothing for medical workers.
The Western Health Trust approached the firm on Friday to help meet a shortage of scrubs.
Staff at the factory worked over the weekend to create samples and begin production.
Initially they are making maroon tops and trousers for GPs at the Covid-19 centre at Derry’s Altnagelvin Hospital which opened on Wednesday.
They have also made face masks for health staff in the local community.
O’Neill’s managing director Kieran Kennedy said it was good to be able to help the frontline services.
“A lot of our friends, a lot of our families are involved in health services,” he said.
“We’re just trying to help people as best we can.”
Mr Kennedy said it was relatively easy to switch production from sportswear to scrubs.
He added the response for staff to meet the new challenge has been “overwhelming”.
Workers are observing social distancing on the factory floor, as well as wearing facemasks and washing their hands.
The firm has brought back 150 workers to make 100,000 sets of scrubs, but more workers could return as orders from other health trusts are expected to grow.
Mr Kennedy said he has been asked to make other items such as aprons and surgical hats.
Although completely different to anything the company has done before, it is an example of how businesses are adapting to help the NHS in the fight against Coronavirus.
He said a lot of firms had already stepped up to the mark and he appealed to all companies that can help out to do whatever they can to assist.