There could be four more symptoms of coronavirus in addition to classic ones such as a new persistent cough and a fever.
A study involving more than one million people in England revealed chills, a loss of appetite, headaches and muscle ache are extra symptoms linked with contracting Covid-19.
The findings are based on swab tests and questionnaires collected between June 2020 and January 2021 as part of the Imperial College London-led React study.
Having any of the other symptoms or the classic ones, either alone or in combination, was associated with infection with Covid-19.
The more symptoms people showed the more likely they were to test positive but around 60% of those with the virus did not report any signs in the week leading up to taking a test.
People in England are currently encouraged to get a Covid-19 test if they have any of the classic symptoms which also includes losing your sense of smell and taste.
The researchers estimate that if everyone who had classic symptoms were tested, it would pick up around half of all symptomatic infections.
But they say that if the additional symptoms were included, this could be improved to three-quarters of symptomatic infections.
The study also found that there was a variation in symptoms depending on a person’s age.
Chills were linked with testing positive across all ages, while headaches were reported in children aged five to 17.
A loss of appetite was reported more in 18-54 year olds and those aged 55 and over.
Muscle aches were mostly reported in people aged between 18 and 54.
According to the study, children were also less likely to report of a fever, a persistent cough and appetite loss compared with adults.
Professor Paul Elliott, director of the React programme at Imperial, said: “These new findings suggest many people with Covid-19 won’t be getting tested – and therefore won’t be self-isolating – because their symptoms don’t match those used in current public health guidance to help identify infected people.
“We understand that there is a need for clear testing criteria, and that including lots of symptoms which are commonly found in other illnesses like seasonal flu could risk people self-isolating unnecessarily.
“I hope that our findings on the most informative symptoms mean that the testing programme can take advantage of the most up-to-date evidence, helping to identify more infected people.”
The study, which has not yet been peer-reviewed, also looked at whether the emergence of the UK’s new coronavirus variant, first identified in Kent, was linked with a different profile of symptoms.
Researchers looked at self-reported symptoms and swab test results collected for the React study in November – December, when PHE estimated the variant made up around 16% of infections.
They compared this with similar data collected in January, when an estimated 86% of infections were from the variant.
While, according to the study, symptoms were broadly similar – in January, compared to November – December, loss or change to one’s sense of smell was less predictive of having Covid-19.
But the proportion of people testing positive with a new persistent cough appeared higher, in keeping with findings from the Office for National Statistics.