However, the study explains this number could in fact be much higher for two predominant reasons. Firstly, testing was prioritised for those who were displaying symptoms of COVID-19 – meaning they could have missed lots of people who had COVID-19 but weren’t showing symptoms. Secondly, the majority of passengers were 60 years and older, who are more likely to experience more symptoms.
Other research suggests the percentage of asymptomatic cases is much higher.
The US Centers for Disease Control and Prevention (CDC) estimates that as many as 25 per cent of people infected with COVID-19 won’t develop any symptoms. That’s one in four cases.
In any case, that is a significantly higher proportion than what the World Health Organisation originally reported. In February, they said asymptomatic cases were “relatively rare”, and accounted for 1-3 per cent of coronavirus cases.