The two most common symptoms of Covid-19 have changed since the pandemic began, a new study claims.
Coronavirus experts had previously warned people to to look out for a new cough, a high temperature and a loss of smell.
But new data shows the advice could be outdated - and hundreds of undiagnosed people could be unknowingly spreading the virus.
The most common symptoms to look out for are now a sore throat, headache and runny nose in those under 40, according to the ZOE Covid Symptom Study.
Data suggests that the Delta variant, first detected in India, feels like a “bad cold”, according to Tim Spector of King’s College London who is leading the work.
For those who are over the age of 40, the signs to be aware of are a headache, runny nose and sneezing.
The news comes as a leading professor claims the Delta variant, first identified in India, seems to “working slightly differently” to other strains.
But this could also be because the virus is currently causing an epidemic in young people and symptoms vary according to age.
ZOE study has been tracking the outbreak since the first lockdown began in March 2020 by using data from millions of Brits who report their systems through an app.
Prof Tim Spector, the lead on the study, told The Telegraph : “Since the start of May, we’ve been looking at the top symptoms and they are not the same as they were.
“This variant seems to be working slightly differently.”
The most common sign is a headache which has affected 66 per cent of under 40s and 53 per cent of over 40s.
The Covid jab means those over 40 display less signs of having the virus now and their most common signs are very mild but none are the classic three of a cough, fever, or loss of smell.
The app has also recently discovered a loss of taste or smell is no longer in the top 10 symptoms.
Prof Spector fears that many young people may be undiagnosed and spreading the virus further due to a shift in the symptoms as cases are highest and fastest growing in people in their 20s.
The NHS currently advises that you get a free Covid test if you have at least one of the three main symptoms of cough, temperature and loss of taste/smell.
But some medics have been calling for the list to be expanded which means infected people can be diagnosed which will curb the spread of the virus.
Prof Spector said: “Covid is acting differently now it’s more like a cold in this younger population and people aren’t realising this, and people might think they’ve got some sort of seasonal cold and they still go out to parties and they might spread it around.”
The government has now received advice that the Delta (Indian) variant is between 40% and 80% more transmissible than the Alpha (Kent) strain - much higher than first thought.
