The 95-year-old monarch, who is experiencing mild cold-like symptoms, is self-isolating at Windsor Castle.
Concerns for the nation’s longest reigning sovereign have been heightened given her age and recent health scare.
But Buckingham Palace has said the monarch expects to be at her desk continuing light duties over the coming days.
The Queen holds an audience with Boris Johnson most Wednesdays, either in person or by telephone, and has recently been holding one or two diplomatic audiences a week with ambassadors by video-link.
She is following self-isolating guidelines after testing positive on Sunday, but her diagnosis comes as Mr Johnson prepares on Monday to bring an end to the legal duty to self-isolate from next week.
The Queen will also be working from her red boxes, sent to her every day and containing policy papers, Foreign Office telegrams, letters and other state papers from Government ministers and Commonwealth representatives that have to be read and, where necessary, approved and signed.
For company, she has her dogs – her elderly dorgi Candy, corgi puppy Muick and another young corgi.
The monarch, if she feels well enough, is also likely to study the Racing Post.
She had a win on Sunday when her horse Kincardine won the Federation Of Bloodstock Agents Maiden Hurdle at Newbury.
Her diagnosis follows a string of cases among the royal family, with the Prince of Wales meeting his mother in the week he tested positive, and the Duchess of Cornwall also isolating after contracting the virus.
The Queen has only just reached her historic Platinum Jubilee of 70 years on the throne, on February 6.
The Royal Household has its own physicians and the Queen’s doctors will be on hand to take care of and monitor the head of state, with Professor Sir Huw Thomas, head of the Medical Household and Physician to the Queen, expected to be in charge.
The Queen has a number of major engagements coming up next month.
She is set to host the Diplomatic Reception on March 2, where she will meet hundreds of members of the Diplomatic Corps at Windsor.
She is also due to attend the Commonwealth Service at Westminster Abbey on March 14 and then the Duke of Edinburgh’s memorial service, also at the Abbey, on March 29.
Just a few weeks ago, she had begun to resume her normal duties, hosting at Sandringham her largest reception in months, on the eve of her Platinum Jubilee anniversary, and a few days later she held her first in-person audience with the Prime Minister in many weeks.
She now regularly uses a stick and recently commented about her mobility issues, telling two senior military officers during a Windsor Castle reception “Well, as you can see, I can’t move,” when asked how she was.
The Queen, whose husband, Philip, died 10 months ago, spent much of the pandemic in the safety of Windsor Castle.