The monarch, 95, tested positive for the virus on Sunday, and had audiences via video-link planned for yesterday.
The Palace said she would still continue with light duties, but it is understood further engagements over the coming week will be decided on nearer the time.
A Buckingham Palace spokesman said: “As Her Majesty is still experiencing mild cold-like symptoms she has decided not to undertake her planned virtual engagements today, but will continue with light duties.”
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Concern for the nation’s longest-reigning sovereign will be at peak levels given her age, her Covid diagnosis and recent health scare.
She had continued working, issuing a message of condolence to the Brazilian president over flooding in his country while self-isolating at Windsor Castle on Monday.
But these are now likely to be under review, as will the major engagement the Queen has next week.
She is set to host the Diplomatic Reception on March 2, where she will meet hundreds of members of the Diplomatic Corps at Windsor.
The Queen 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.
The Royal Household has its own royal physicians and the Queen’s doctors will be keeping a close eye on the head of state and monitoring her progress, with Professor Sir Huw Thomas, head of the Medical Household and Physician to the Queen, expected to be in charge.
The Queen has only just celebrated her Platinum Jubilee of 70 years on the throne, reaching the milestone on February 6.
She is believed to be triple vaccinated but until recently had been on doctors’ orders to rest and only undertake light duties since mid-October.
She cancelled a run of major engagements, and also secretly spent a night in hospital on October 20 undergoing preliminary tests.
She now regularly uses a walking stick and has been pictured recently looking frailer.