Latest Coronavirus News
If you have no symptoms of the COVID-19 virus, can you pass the disease to others?
The medical establishment used to think (and mostly still does) that people with asymptomatic coronavirus infections might be contagious like infected people with coughs and fevers. But news from the World Health Organization this week muddied the waters, underscoring how baffling the deadly new disease has been for clinicians and researchers worldwide.
Further confusion comes from the potential for people to spread the virus after they are infected, but prior to showing clear symptoms. These pre-symptomatic people may be able to spread the virus to others for up to three days before a telltale cough or fever develops, and this accounts for an estimated 40% of virus transmission, according to preliminary CDC estimates.
- Asymptomatic: An infected person who never shows signs or symptoms of infection. In some studies, people with subtle, mild symptoms have been included in this definition.
- Pre-symptomatic: An infected person who will eventually develop symptoms, but so far has not.
Headlines have focused on the WHO‘s Dr. Maria Van Kerkhove, who leads the emerging disease and zoonosis unit. She claimed—then backed away from the claim—that spread of coronavirus from people who never develop symptoms is “very rare.” Meanwhile, much of the popular press ignored two studies on the topic that seem to contradict her earlier statement.
“From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual,” Dr. Van Kerkhove said Monday. “We have a number of reports from countries who are doing very detailed contact tracing. They're following asymptomatic cases, they're following contacts, and they're not finding secondary transmission onward.”
Her comments were met with immediate skepticism by WHO colleagues, and Dr. Van Kerkhove backpedaled the next day, calling asymptomatic spread a “really complex question.” She also said it was “misunderstanding to state that asymptomatic transmission globally is very rare.”
On Wednesday, Dr. Anthony Fauci called the statement “not correct” on ABC’s Good Morning America, and pointed out that between 25% and 45% of those infected never show symptoms.
What made this statement so controversial? And what data are available to help understand the spread of COVID-19 from an asymptomatic carrier of the disease?
Studies Suggest Asymptomatic Carriers Still Contagious
As many as 86% of the people initially infected in Wuhan, China became sick from people who were not sick enough to visit the doctor, scientists found in a paper published in Science May 1. These could have been people with no symptoms (asymptomatic) or people who had mild enough symptoms that they caused little concern.
This study was co-authored by Jeffrey Shaman, a professor at Columbia University who forecasts infectious disease outbreaks. His study focused on those infected before Wuhan entered an unprecedented lockdown to stop further infection.
The paper concluded that people without any documented symptoms (which could include people with mild symptoms) were about half as infectious as people with serious symptoms, but together they caused a majority of new infections, Shaman told Bloomberg.
At the end of May, researchers in Wuhan, China published a study of 78 people who were exposed to the Huanan seafood market or who had close contact to another patient with COVID-19. All were infected with SARS-CoV-2, the virus that causes COVID-19.
In the study, 45 patients showed symptoms like fever, dry cough, and fatigue, while 33 showed no symptoms. All of the subjects were hospitalized and tested every day for symptoms and signs of infection.
Meanwhile the patients’ close contacts were also monitored using CT scans and nasal swabs.
The asymptomatic patients were different in several ways. They tended to be younger, were more likely to be female, and their nasal swabs showed a shorter duration of viral shedding.
Nevertheless, infected people without symptoms were shown to be contagious in a window of time lasting anywhere from three to 12 days, with eight days being the average. So without any apparent symptoms, these virus carriers could continue shedding and spreading SARS-CoV-2 for about a week, the study suggests.
On the other hand, in her initial comments, Dr. Van Kerkhove alluded to unpublished data from countries worldwide that WHO has access to. If these data present a different narrative from the one available in the published literature, the policy implications could be enormous. Experts agree that further study is necessary to guide both policy and public health responses as the pandemic continues.