Four new coronavirus symptoms have been linked to COVID-19 by researchers in the UK.
Instead of the well-known symptoms - coughing, fever and a loss of smell and/or taste - for some the first sign of a COVID-19 infection could be a chill, a headache, aching muscles or a loss of appetite.
More than 1 million Brits who were tested for the virus between June 2020 and January also filled out a questionnaire about their symptoms.
According to researchers at Imperial College London, if people only showed up for a test when they developed the "classic" signs of infection, only around half of all symptomatic cases would be picked up. Others showing signs of the new symptoms might think they just have a typical cold instead.
Three-quarters of all symptomatic infections would be picked up if people suffering just one of the newly identified symptoms also got themselves tested, they estimate.
"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," said Prof Paul Elliott, director of the college's REACT study.
"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."
But the more symptoms people were showing from the new list, the more likely they were to test positive.
Complicating matters, different age groups also tended to show different symptoms. While chills were consistent across all age groups, children were most likely to report headaches and less likely to report fever, coughs and loss of appetite, while muscle aches mostly affected young adults.
It's hoped the discovery of the new symptoms will help health authorities rein in the more infectious B.1.1.7 variant of the virus, picked up in Kent late last year and fast taking over as the dominant strain. Only 16 percent of infections in November and December were B.1.1.7, rising to 86 percent in January.
"While symptoms were broadly similar, in January compared to November-December loss or change to sense of smell was less predictive of having COVID-19, while the proportion of people testing positive with a new persistent cough appeared to be increased."
Joshua Elliott of Imperial College London's School of Public Health said the virus will keep changing, and it's vital research keeps up.
"As the epidemic progresses and new variants emerge, it's essential that we keep monitoring how the virus affects people so that testing programmes meet changing needs."
In recent weeks evidence has begun to emerge in addition to being more infectious, B.1.1.7 could be up to 30 percent more deadly. Luckily the existing vaccines - trained to combat the original strain - appear to work just as well against B.1.1.7, though it's still early days in terms of data collection.
The UK has the world's fifth-highest death toll from COVID-19. To date, there have been almost 115,000 deaths and just shy of 4 million confirmed cases.
"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," said Prof Elliott.
