Headaches, a sore throat and a runny nose appear to be the most common reported symptoms by those suffering with the Delta variant of Covid.
The findings, collated by the ongoing Zoe Covid Symptom Study, suggests the Delta variant - formerly identified as the Indian variant - behaves more like a bad cold.
It relegates the earlier Covid symptoms of a cough and loss of taste and smell.
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Professor Tim Spector, who runs the study, said: "Covid is … acting differently now, it’s more like a bad cold in this younger population.
"People might think they’ve just got some sort of seasonal cold, and they still go out to parties … we think this is fuelling a lot of the problem."
He added: "So, what’s really important to realise is that since the start of May, we’ve been looking at the top symptoms in all the app users, and they’re not the same as they were.
"So, the number one symptom is headache … followed by sore throat, runny nose and fever."
The Delta variant now accounts for 90% of all new cases of coronavirus in the UK, according to the most recent data from health secretary Matt Hancock.
Further research also indicates the variant is 60% more transmissable than the previously dominant Alpha - or Kent - variant, says Public Health England.
There are a range of symptoms associated with Covid but government advice states the main ones are:
a high temperature – this means you feel hot to touch on your chest or back (you do not need to measure your temperature)
a new, continuous cough – this means coughing a lot for more than an hour, or 3 or more coughing episodes in 24 hours (if you usually have a cough, it may be worse than usual)
a loss or change to your sense of smell or taste – this means you've noticed you cannot smell or taste anything, or things smell or taste different to normal
The Zoe Covid Symptom Study collects information via its app from more than 4.6 million people worldwide to track the virus and data is shared with researchers at King's College London and the NHS.
"I think the message here is that if you’re young and getting milder symptoms any way, it might just feel like a bad cold or some funny feeling … do stay at home and do get a test," Prof Spector said.