But anosmia, a loss of taste and smell, was later added to the list of symptoms to look out for.
The new research looked at data from healthy participants who then got sick with COVID-19.
The researchers said identifying people who were potentially infected with the virus from a population of sick people calling NHS 111 “is problematic”.
They warned a new model is needed to effectively track and trace symptoms, and added they would be “happy to build” such a thing.
The researchers added: “It would likely use anosmia amongst other signals, and be optimised for symptoms across the first few days to maximise sensitivity.”
As part of the research, the ZOE app collected data from 2.5 million users across the UK.
During the duration of the study, 116, 568 users became sick and 727 users tested positive for COVID-19.
Data from the first day showed the same number of people logged a fever as a loss of sense of smell.
The researchers said: “This data shows that fever or cough are not present in the first few days for most people with COVID.
“The distributions of symptoms for users who tested positive are quite different from the overall population.
“If we want to identify people for early testing, when viral shedding high, we should build a new model optimised for data in just the first few days”.
The research follows advice from scientists at King’s College London who say anosmia should form part of screening measures for COVID-19.
What to do if you have symptoms of COVID-19
If you experience either a high temperature, a new, continuous cough, or loss of change to your sense of smell or taste, the NHS recommends you use the 111 online coronavirus service.
You should not go to places like a GP surgery, hospital or pharmacy.
If you cannot get help online you can call 111.
If your symptoms are mild you will most likely be advised to not leave home (self-isolation).
Anyone with symptoms must self-isolate for seven days from when their symptoms started.
Anyone in your home who does not have symptoms must self-isolate for 14 days from when the first person started having symptoms.