A study of over a million people in England has revealed additional symptoms caused by the coronavirus than just a cough, fever, and loss of taste or smell.
Chills, loss of appetite, headache and muscle aches were together most strongly linked with being infected.
Having any of these other symptoms alone was associated with COVID, or in combination with the classic signs.
The more symptoms people showed the more likely they were to test positive. The findings come from swab tests and questionnaires collected between June 2020 and January 2021 as part of the Imperial College London-led REACT study.
People in England are currently encouraged to take a Covid-19 test if they have at least one of the classic symptoms.
The researchers said based on their findings, current testing would pick up around half of all symptomatic COVID cases if everyone eligible were tested.
But this would rise to three-quarters of symptomatic cases if testing eligibility expanded to those with symptoms such as chills.
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 found symptoms of COVID varied with age.
Chills were found in people of all ages. But headaches were most common in children and teenagers.