About 1.3 million people in the UK have "long Covid", symptoms lasting more than four weeks after an initial infection, an Office for National Statistics survey suggests.
Of those, 892,000 (70%) first caught the virus at least 12 weeks ago and 506,000 (40%) at least a year ago.
The survey asked nearly 352,000 people to record their own symptoms.
There is no universally agreed definition of long Covid and different studies use varying definitions.
Guidance for health workers in England describes it as symptoms that continue for more than 12 weeks after an infection cannot be explained by another cause.
These include extreme tiredness, shortness of breath, heart palpitations and "brain fog", according to the NHS.
The ONS survey, over four weeks in November and December 2021, suggests, of those with long Covid:
51% have fatigue
37% have loss of smell
36% have shortness of breath
28% have difficulty concentrating
In line with previous analyses, about 20% said their symptoms meant their ability to do day-to-day activities had been limited a lot.
And those most likely to have long Covid are:
35- to 69-year-olds
people with underlying conditions
those working in health, social care and education
University of Exeter senior clinical lecturer Dr David Strain said: "The stark warning here is that, based on this, in the previous waves, over 800,000 people have their day-to-day activities significantly affected over three months after catching Covid and nearly a quarter of a million report this has a dramatic impact on their quality of life.
"As we continue to see case numbers of Omicron rise, we must be wary that our reliance purely on hospitalisations and death as a measure of the risk from Covid could grossly underestimate the public-health impact of our current Covid strategy."