40–45% infected with coronavirus are asymptomatic, study confirms


A new study warns that around 40–45% of people who contract SARS-CoV-2 most likely remain symptom-free. Such cases may contribute to the “silent spread” of the virus. Moreover, even asymptomatic people may experience long-term respiratory issues, the study authors caution.

person in city center wearing face mask
Researchers warn that many SARS-CoV-2 infections are likely asymptomatic, and they urge people to wear face masks to prevent ‘silent spread.’

In considering the spread dynamics of the new coronavirus — or SARS-CoV-2 — researchers, and health authorities have been pondering the importance of “silent” transmission.

This concept says that people who may have contracted the virus but who do not experience any symptoms could unwittingly contribute to the spread by not realizing they are carriers.

It remains unclear just what the likelihood is of asymptomatic transmission. 

Recently, Dr. Maria Van Kerkhove, Head of Emerging Diseases and Zoonosis at the World Health Organization (WHO), said that this form of transmission was “rare,” though later, she and her colleagues revised that statement in a Q&A session.

Now, a new study from the Scripps Research Translational Institute in La Jolla, CA, emphasizes just how many cases of SARS-CoV-2 infection are asymptomatic.

Its authors, behavioral scientist Daniel Oran and Dr. Eric Topol, professor of Molecular Medicine at Scripps Research, warn that the high proportion of asymptomatic infections may contribute to the wide transmission of the virus.

Furthermore, they warn that even people who have not experienced any symptoms may still face long-term effects following exposure to the virus.

The two researchers present their work in a study paper now featuring in Annals of Internal Medicine.


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