At a meeting of the science and technology committee today, Dr Angelique Coetzee told MPs details of what she had been witnessing from patients she was treating.
"The picture predominantly for the past four weeks stays exactly the same, the three major complaints will be: what we would call myalgia (sore muscles, body ache and pain), headache as well as a little bit of a fatigue for a day or two."
The UK's official list of three symptoms has not changed since May 2020, when a loss of taste and smell was added to high temperature and a new, continuous cough.
Coetzee said in South Africa they are "running a campaign" for people to get tested even if they wake up with a "slight headache".
"If you wake up this morning, and you have this headache and the myalgia, it would be prudent to wait 24 hours for the rapid test," she said.
"We have found that the rapid test can be still false negative in that first period, less than 24 hours, but after 24 hours, up until about 5 to 6 days later, the rapid test is more than sufficient to be able to detect positive cases."
On Monday, Boris Johnson's spokesperson said there are no plans to change official guidance on COVID symptoms for Omicron, despite the growing anecdotal evidence that they differ from the signs associated with previous variants
“We take clinical advice and there is a balance to be struck between widening the symptoms too much that you include other illnesses," he said.
"But we are confident we continue to strike the right balance in terms of the symptoms that people look out for in terms of what is accounted for - but obviously, we will make any changes if required and advice clinically."
On Friday, Professor Tim Spector, from the COVID monitoring Zoe app, said that Omicron cases are being missed because symptoms manifest themselves differently.
“Omicron is probably more, much more similar to the mild variants we’re seeing in people who have been vaccinated with Delta than anything else,” he told BBC Breakfast.
“And so it is going to be producing cold-like symptoms that people won’t recognise as COVID if they just believe the official Government advice.”
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The comments come amid mounting speculation over the virulence of the emerging variant, which is spreading rapidly across the country - with some modelling suggesting there are 200,000 new cases each day in the UK alone. The variant has become the dominant variant in London and is believed to be more contagious than previous strains.
PCR tests were temporarily unavailable across England on Tuesday morning thanks to "exceptionally high demand", officials said.
Twice on Tuesday, the government website said there were no slots available for PCR tests at walk-in and drive-in test sites across every region of England, before making more slots available.
Omicron has triggered concern globally, prompting the government's reintroduction of certain social distancing measures in an attempt to slow the spread of the virus while they accelerated the booster programmes.
Early data suggests a third jab is necessary to provide adequate protection against the new variant and avoid hospitalisations, leading the government to expand capacity and postpone non-urgent NHS appointments to get jabs in arms.
However England’s chief medical officer Professor Chris Whitty warned Cabinet on Monday that a “significant increase in hospitalisations” from Omicron is expected in the coming weeks.
The first death of a patient with Omicron was recorded yesterday, with 4,713 confirmed cases of the new variant.
COVID-19: Omicron currently infecting 200,000 a day - as COVID passport changes announced