This Is Who's Transmitting 45 Percent of Coronavirus Cases, Study Says

Recent studies show these people are spreading COVID-19 at alarming rates.

Few bits of breaking news have caused as much of a stir as the recent comments made by the World Health Organization (WHO) regarding the spread of coronavirus. After publicly stating that asymptomatic transmission of COVID-19 was "very rare," WHO drew criticism from the medical community and walked back on the statements soon thereafter. But in the process, we all learned one very important lesson: There's an important distinction between asymptomatic carriers and pre-symptomatic ones. Asymptomatic patients are those who are infected but never develop noticeable coronavirus symptoms, while those who are pre-symptomatic are infected but have yet to develop symptoms. And it's the second group we may need to be most worried about. According to a recent study, patients who have yet to show symptoms are responsible for transmitting nearly half of coronavirus cases.

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An April report out of China, published in the journal Nature Medicine, found that "44 percent of secondary cases were infected during the index cases' pre-symptomatic stage." Translation? Nearly half of coronavirus cases stem from those who are sick before their symptoms even appear. Based on these findings, the authors suggest that "disease control measures should be adjusted to account for probable substantial pre-symptomatic transmission."

This report mirrors what has been found in other studies that seek to gauge the most contagious points in the virus's infection cycle. According to another recently published study in the journal Eurosurveillance, data collected showed that 48 percent of cases in Singapore and 62 percent in Tianjin, China, were caused by pre-symptomatic individuals.


Another study, also published in the journal Nature Medicine and conducted by researchers out of WHO's Collaborating Centre for Infectious Disease Epidemiology and Control in China, found that patients are most likely to spread COVID-19 up to 72 hours before they show signs of having contracted the virus.

That's part of the reason why coronavirus is so difficult to track and control. The authors of these studies urge the medical community and public officials to use effective preventative measures, such as contact tracing, to prevent new outbreaks from developing. And for more on how COVID-19 spreads, check out The Surprising Thing Making Coronavirus Up to 10 Times More Infectious.

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Zachary Mack
Zach is a freelance writer specializing in beer, wine, food, spirits, and travel. He is based in Manhattan. Read more
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