"They may be silent transmitters and they don't know about it - and so I think that's a problem," she said.
"You may have a lot of people out in society and they're not self-isolating because they didn't know that they are positive."
University students, she said, should be tested regularly and definitely before they went home for Christmas.
"I think you could seed a lot of new infections around Christmas - you're indoors, you sit around the table. Hopefully they can get that [testing] up and running before Christmas. I don't think they should wait until Christmas."
The researchers argued for a change in testing strategy.
"Covid-19 symptoms are a poor marker of infection," they wrote in the journal Clinical Epidemiology.
"In order to capture 'silent' transmission and potentially prevent future outbreaks, test programmes should involve frequent and widespread (Covid-19) testing of all individuals, not just symptomatic cases, at least in high-risk settings or speciic locations."
Professor Tim Spector, a genetic epidemiologist at King's College London, who leads the Covid Symptom Study app, said data from more than four million people who used the app and reported symptoms over a week found that 85 per cent of adults reported fever, cough or loss of taste/smell.
"But the data on children and the over-65s tell us a different story," he added.
"Only using the UK's three classic symptoms will miss around 50 per cent of cases in these important groups that were included in the ONS survey.
"In a sub-study at King's College London of twins using antibody testing and the ability to report 20 different symptoms, we showed that only 19 per cent of people are truly asymptomatic."