Estimates of asymptomatic coronavirus cases are around 40-45% according to Dr. Anthony Fauci, with the World Health Organization previously projecting a similar estimate, though a new study suggests silent spreaders could comprise more than three-quarters of cases.
Researchers from University College London published their peer-reviewed findings on Thursday in Clinical Epidemiology.
“Little is known about what proportion of infectious people are asymptomatic and potential ‘silent’ transmitters,” study authors wrote. They used data from the Office for National Statistics Coronavirus (COVID-19) Infection Survey pilot study, which surveys households in England.
Up to 86% of infected individuals reported no symptoms specific to COVID-19 when they were tested, per the study. (iStock)
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Of 36,061 people who were tested between April 26 and June 27, 625 (1.7%) reported symptoms on the day of the test. Of the total, just 115 people tested positive, and of those, 76.5% reported no symptoms when they were tested, while 86% listed no symptoms specific to COVID-19.
The study focused on “core” symptoms like cough, fever and loss of taste or smell.
Researchers said the findings suggest that symptom-based testing will not fully capture silent, or asymptomatic, transmission, and “our analyses suggest that asymptomatic cases of COVID-19 were widespread in the UK in Spring 2020.”
They called for a change in future testing strategies to prevent future outbreaks and advised frequent, widespread testing regardless of symptoms. They said this could be possible by developing “simpler tests that produce rapid results at low cost, accepting some loss of sensitivity.”
Nevertheless, the Centers for Disease Control and Prevention (CDC) advises confirming results from rapid tests with a more sensitive test like an RT-PCR/nasal swab. The agency also advises 14-day self-quarantine following exposure or travel, even if virus tests return negative.