In a new study, researchers found that more than 40% of people diagnosed with COVID-19 in one Italian town showed no signs of being ill.
This means that asymptomatic carriers may be significant spreaders of the virus.
The research shows how important mass testing and isolating carriers were in containing clusters of the virus.
The research was conducted by a team at the University of Padua and elsewhere.
The town of Vo, population 3,200, registered Italy’s first death from the disease in late February.
It was immediately placed in a two-week lockdown, during which researchers were able to test more than 85 percent of the population for COVID-19.
In the study, the team found that 2.3% of Vo was infected at the beginning of quarantine, compared with 1.2% at the end of lockdown, and that more than 40% of those who tested positive showed no symptoms.
The team says their findings showed how rapid case isolation and mass testing was able to effectively eliminate the virus from Vo.
The team also found that asymptomatic COVID-19 carriers had a similar viral load to those who got sick, suggesting that while not ill themselves they could still spread the virus.
This was particularly important for policymakers seeking to limit COVID-19 clusters from spreading.
Asymptomatic infection is entirely unconscious of carrying the virus and, according to their lifestyle and occupation, could meet a large number of people without modifying their behavior.
The data from Vo also showed that none of the children under the age of 10 tested positive for COVID-19 despite living with several adults who did.
One author of the study is Andrea Crisanti from the Department of Molecular Medicine of the University of Padua and the Department of Life Sciences at Imperial College London.
The study is published in Nature.
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