“Christmas will be tough this year. I don't think it's going to be the usual celebration it is and all families coming together, I'm afraid,” he told Sky News' Sophy Ridge On Sunday.
”I think we have to be honest and realistic and say that we are in for three to six months of a very difficult period.
“The temperatures drop, we are all indoors more often, we have the other infections that come this time of year. It's much better for us to be upfront and honest now.”
But Professor Farrar said he thought coronavirus vaccines and working treatments were “three to six months away”.
It comes after Boris Johnson warned a “normal Christmas” was at risk when he announced the most recent rules to tackle the spread of Covid-19.
Emphasising the importance of obeying social distancing, wearing masks and handwashing to contain the virus, the prime minister said: “All that basic stuff is essential if we’re going to come out of this and allow people to have anything like a normal Christmas.”
It came after Culture Secretary Oliver Dowden said the purpose of the government's new three-tier lockdown structure is to reign the virus in hopefully ahead of the festive season.
“The purpose of doing this is to ensure that we get the virus under control so that by the time we get through to after Christmas we are in that position where it's under control,” he told Kay Burley earlier in the month.
”Indeed I hope it will be sooner than that.“