US infectious disease expert Dr Anthony Fauci has been the victim of threats and harassment, he told Ryan Tubridy on RTÉ's Late Late Show last night.

He also spoke of his optimism that a safe and effective vaccine could go into production before the end of 2020. 

Dr Fauci said he approved of implementing restrictions on parts of society in order to stop the spread of coronavirus. But not everybody agreed with this.

The Director of the National Institute of Allergy and Infectious Diseases revealed: "I myself have been physically threatened and harassed and my family have been harassed.

"The enemy is the virus - the enemy is not the public health people who are trying to contain the virus."

Dr Fauci, speaking via a video link, also said scientists across the world were working "very aggressively" on multiple vaccines.

"We should know by the end of 2020, by November or December, whether we have safe and effective vaccines which can then start to be deployed."

In the future, once there is a vaccine, he said "we won't be completely avoiding public health measures but clearly they will be much less restrictive".

He said Covid-19 cases in the US were now levelling off at around 40,000 cases a day. "As we move into the winter months, where there will be much more indoor activity, that could be problematic. We have got to do better than that."

He added: "We got hit badly, worse than most countries, Ireland did not get as hit as bad but you did get hit bad and what you did is that you put restrictions that were substantial restrictions and you got a baseline back down."

Asked about his relationship with President Donald Trump, Dr Fauci said it was "good" but there had been some tension. "There have been some issues upon which we disagree."

If Mr Trump says something negative about him on Twitter, he insisted: "I do not take it personally, I do my job. I just have to tell the truth and go by the science."

Dr Fauci said people need to pull together in a society to deal with Covid-19 and admitted it was "painful and frustrating" to see large crowds gathering at US political rallies while ignoring public health guidelines.

"Adherence, or not, to these has almost turned into a political statement in the US," he said.

"With an infectious disease, you can't consider yourself in a vacuum and say 'well I don't really care if I get infected because I'm a young person and it's likely that I will not have any serious consequences'.

"A high percentage of people who get infected are asymptomatic but the thing you forget is, by getting infected, even if you are without symptoms, you are inadvertently propagating the outbreak," said Dr Fauci.