The Queen has held her weekly telephone audience with the prime minister despite having COVID-19, Buckingham Palace said.
The monarch, 95, has been suffering mild COVID symptoms after testing positive for the virus on Sunday.
A Buckingham Palace spokesman said: “Her Majesty did speak to the prime minister this evening.”
On Tuesday, she cancelled her planned virtual engagements.
The Queen, who has avoided catching COVID for the best part of two years, has spent much of the pandemic in the safety of Windsor Castle, where there has been a tightly-controlled and limited rota of staff nicknamed “HMS Bubble”.
Celebrations for her Platinum Jubilee of 70 years on the throne – a milestone reached on 6 February – begin in June.
Her Majesty, the UK’s longest reigning monarch, recently spent more than three months resting on doctors’ orders.
She withdrew from attending the COP26 climate change summit in Glasgow, the Festival of Remembrance and the Remembrance Sunday Cenotaph service in the autumn after suffering a sprained back.
Next week, the Queen is due to host the Diplomatic Reception and meet hundreds of dignitaries at Windsor.
She and Boris Johnson – the 14th prime minister during her reign – hold a weekly audience on Wednesdays following Prime Minister’s Questions in the Commons.
The call has largely been by telephone throughout the pandemic.