In this 2015 file photo, Dr. Yvonne Doyle speaks at City Hall in London. Keith Larby/Alamy Live News

Chinese health officials said Sunday that the coronavirus can be spread before any symptoms appear, meaning carriers may not realize they are infected before they transmit the virus to others.

There's still lots we don't know about this outbreak, however, and according to Dr. Yvonne Doyle, medical director of Public Health England, "it isn’t confirmed that people are infectious before they appear to be ill."

"That's one of the things we have to learn," she added.

Here's an excerpt (lightly edited for clarity) of Dr. Doyle's interview with BBC Radio 4's Today Program on Monday:

Q: (We're) hearing from China that people can spread the virus without having any symptoms...

A: At the moment we don’t have confirmed evidence that that’s the case. It's reasonable of course to assume that could happen, but at the moment we don’t know that, because this is a novel virus.

Q: Do you think it is likely that we are going to see cases (in the UK)?

A: Yes I do... I think I would be surprised if there wasn’t. We are well prepared since we spotted this in the early new year. We have been working with increasing intensity with the NHS (National Health Service) to make sure we are well prepared, and we are.

Q: (We're) also hearing Chinese officials are also developing a vaccine, will that be ready in time?

A: It won’t be ready in time at the moment. Vaccines take months, maybe years to develop.