In a new study, researchers found that many people infected by the virus behind the ongoing deadly COVID-19 pandemic never show symptoms of the disease.
The findings suggest that asymptomatic infections may account for as much as 45 percent of all COVID-19 cases, playing a significant role in the early and ongoing spread of COVID-19.
The report highlights the need for expansive testing and contacts tracing to mitigate the pandemic.
The research was conducted by a team at Scripps Research.
In the study, the team collected information from testing studies on 16 diverse cohorts from around the world.
These datasets—gathered via keyword searches of PubMed, bioRxiv, and medRxiv, as well as Google searches of relevant news reports—included data on nursing home residents, cruise ship passengers, prison inmates, and various other groups.
The team found what virtually all of them had in common was that a very large proportion of infected individuals had no symptoms
Among more than 3,000 prison inmates in four states who tested positive for the coronavirus, the figure was astronomical: 96 percent asymptomatic.
The review further suggests that asymptomatic individuals are able to transmit the virus for an extended period of time, perhaps longer than 14 days.
The viral loads are very similar in people with or without symptoms, but it remains unclear whether their infectiousness is of the same magnitude.
To resolve that issue, scientists will need large-scale studies that include sufficient numbers of asymptomatic people.
The authors also conclude that the absence of symptoms may not imply an absence of harm.
CT scans conducted on 54% of 76 asymptomatic individuals on the Diamond Princess cruise ship, appear to show significant subclinical lung abnormalities raising the possibility of SARS-CoV-2 infection impacting lung function that might not be immediately apparent.
The scientists say further research is needed to confirm the potential significance of this finding.
An asymptomatic individual is someone who is infected with SARS-CoV-2, but never develops symptoms of COVID-19, while a pre-symptomatic person is similarly infected, but will eventually develop symptoms.
Longitudinal testing, which refers to repeated testing of individuals over time, would help differentiate between the two.
One author of the study is Eric Topol, MD, founder and director of the Scripps Research Translational Institute and professor of Molecular Medicine at Scripps Research.
The study is published in the Annals of Internal Medicine.
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