More than 40% of people infected with coronavirus in a small village in northern Italy had no symptoms during a coronavirus outbreak earlier this year, an international team of researchers reported Tuesday.
Yet the people without symptoms had virtually the same viral load – that’s the amount of virus in their systems – as people who did have symptoms, the researchers wrote in a pre-print, non-peer reviewed report published in the journal Nature.
The team tested most of the residents of Vo after an outbreak forced a two-week lockdown of the village in February.
They found 42.5% of people with confirmed Covid-19 infections were asymptomatic, meaning they “did not have symptoms at the time of the swab testing and did not develop symptoms afterward,” researchers Enrico Lavezzo and Elisa Franchin of the University of Padova in Italy and colleagues across Europe wrote. “On the first survey, which was conducted around the time the town lockdown started, we found a prevalence of infection of 2.6%, they wrote. “On the second survey, which was conducted at the end of the lockdown, we found a prevalence of 1.2%.”
This is the first definitive assessment of the rate of asymptomatic infection in Covid-19 cases since the pandemic began, Lavezzo and Franchin’s team said.
“This figure is of enormous value as it informs estimates and decisions regarding the further dealing with the epidemic in many countries,” they wrote.
“This study sheds new light on the frequency of asymptomatic SARS-CoV-2 infection, their infectivity (as measured by the viral load) and provides new insights into its transmission dynamics and the efficacy of the implemented control measures,” they added.