A government health expert has said she is "not convinced" the Delta variant has new COVID-19 symptoms despite researchers claiming it was presenting different signs of infection.
At the moment, the NHS lists "a new continuous cough, a high temperature, loss of or change in smell or taste" as main COVID-19 symptoms.
But research from the Zoe COVID Symptom study suggested symptoms for the virus may be changing due to the Delta variant, which was first identified in India.
According to the data, headaches, sore throats and a runny nose were now the most reported symptoms from people infected with coronavirus.
But on Wednesday, during a Downing Street press conference, PHE’s head of immunisation Dr Mary Ramsay told reporters she was not “convinced yet” the Delta strain was causing different signs of infection.
She said: "I don't think any evidence that we are missing cases."
Watch: Nadhim Zahawi celebrates milestone of three-fifths (60%) of UK adults being fully vaccinated
Professor Tim Spector, who is in charge of Zoe COVID Symptom study, told the BBC: “Since the start of May, we have been looking at the top symptoms in the app users – and they are not the same as they were.”
He added: “People might think they’ve just got some sort of seasonal cold and they still go out to parties and they might spread it around to six other people.
“We think this is fuelling a lot of the problem.”
The Imperial College London React study also showed other symptoms linked to COVID-19, including muscle aches, chills, headache and loss of appetite.
It comes as vaccines minister Nadhim Zahawi celebrated the milestone of three-fifths (60%) of UK adults having received both vaccine doses.
On Wednesday, he said more than 14,000 lives have now been saved by vaccines, while 44,500 hospital admissions had also been averted in England, including 2,500 in the past two weeks.
Zahawi added he is confident the government will meet its target of double vaccinating two-thirds (66%) of adults by 19 July.
The government is planning to scrap several restrictions for double-vaccinated people.
The plans, first reported by The Times on Saturday, could see fully vaccinated people who come into contact with a COVID-19 carrier being spared the 10-day isolation requirement when contacted by the test and trace system.
Instead, the paper reported, people will be offered the chance to take a test every morning for a week.
Health secretary Matt Hancock confirmed the government “will” scrap the isolation period for double-jabbed people on Monday.
He told BBC Breakfast a pilot had been launched “to check that that will be effective, but it is something that we’re working on”.
Hancock added: “We’re not ready to be able to take that step yet, but it’s something that I want to see and we will introduce, subject to clinical advice, as soon as it’s reasonable to do so.”
Boris Johnson also hinted on Thursday the UK was close to permitting unrestricted travel abroad for fully vaccinated people, in what would be a huge boost for airlines and holiday companies brought to their knees by COVID-19.
Johnson said he was not ruling out going abroad for his summer holiday and said there would be an announcement later on Thursday.
"I think that the whole double jab process is offering the real prospect of opening up to travel, and we'll be setting out a bit more later on," he told reporters.