Two out of five people with COVID-19 are asymptomatic, according to a new study of more than 29 million people. The study, which also compiled data from 95 articles published in the journal JAMA, found that 40.5 percent of positive cases showed no signs of illness. So nearly half of us may have had COVID-19 and be completely unaware of it.
“The high percentage of asymptomatic infections highlights the potential risk of transmission of asymptomatic infections in communities,” the authors write.
Although many COVID cases are asymptomatic, it is also stated that only 0.25% of the tests performed on 29 million people give false results: “Asymptomatic infection screening is required especially for countries and regions that have successfully controlled SARS-CoV-2. Asymptomatic infections should be managed similarly to confirmed infections, including isolation and contact tracing.”
The studies used in the meta-analysis were largely conducted in Europe, North America and Asia, but also included data from Africa and South America. Among the total population tested, most of the asymptomatic infections are in Europe, with Asia having the lowest percentage.
In the population that tested positive for COVID-19, asymptomatic infections were most common in pregnant women and people traveling by plane or on a cruise. The authors argue that screening and quarantine for travelers are therefore important in minimizing community transmission.
Approximately one-third of confirmed asymptomatic COVID-19 cases are healthcare workers or hospital patients, and the importance of measures to prevent the spread in this environment is increasing. The authors reiterated the importance of testing asymptomatic individuals and measures such as personal protective equipment (PPE) and hand hygiene.
Asymptomatic cases were more common in younger people under the age of 39, perhaps because they were less likely to experience more severe symptoms.
However, the study has a few notable limitations. The number of asymptomatic infections may include cases where symptoms have not yet developed. It can also be said that there is a potential publication bias, since studies that do not find evidence of asymptomatic infections are less likely to be published. Both of these limitations mean that the number of asymptomatic infections can be overestimated than they actually are.
Still, the authors hope that their findings will help influence public health measures and ultimately protect people by highlighting how many of the population can become infected and contagious even when they don’t show any symptoms: “Our results can raise awareness among the public and policymakers and provide evidence for prevention strategies.”
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