NEJM study claiming novel coronavirus can be transmitted during incubation period flawed

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Contrary to claims made in NEJM, the Chinese woman did not transmit the novel coronavirus to the German during the incubation period. She had symptoms during her stay in Germany but was tested for the virus only on her return to China.

A Correspondence published on January 30 in the medical journal The New England Journal of Medicine (NEJM) about a Chinese woman infecting a German during the incubation period of the novel coronavirus turns out to be wrong.

China’s National Health Commission Minister had first warned that the novel virus might be spreading even during the incubation period when symptoms do not show up. The NEJM paper confirming it meant that the novel virus indeed has the capability to infect people even before symptoms show up overtly. If it were true, it would mean that there is a possibility that people could spread the virus long before they know they have been infected.

According to the journal Science, Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, told journalists: “There’s no doubt after reading [the NEJM] paper that asymptomatic transmission is occurring. This study lays the question to rest.”

How the truth came out

As per Science, the Robert Koch Institute (RKI), the German government’s public health agency and the Health and Food Safety Authority of the state of Bavaria spoke to the Chinese woman after NEJM published the finding. And it turns out that the Chinese woman did indeed have symptoms during her stay in Germany, when she came in contact with the German who fell sick. But no tests were carried out in Germany to confirm if she was infected with the novel virus. She underwent testing for the novel coronavirus in China after her return from Germany and tested positive for the virus.

So, it turns out that the virus was not transmitted by the Chinese woman during the incubation period and the German man was not infected as a result of such transmission. The transmission had happened after the incubation period and when she was exhibiting symptoms.

Pressure to publish

“I feel bad about how this went, but I don’t think anybody is at fault here,” virologist Christian Drosten of the Charité University Hospital in Berlin, who did the lab work for the study and is one of its authors told Science. “Apparently the woman could not be reached at first and people felt this had to be communicated quickly.”

According to NEJM, the German had attended meetings with a Chinese woman, a business partner of the company, near Munich on January 20 and 21. The Chinese woman, a Shanghai resident, had visited Germany between January 19 and 22. During her stay in Germany, she did not exhibit any signs or symptoms of infection but had become ill on her journey back to China, where she tested positive for coronavirus on January 26.

WHO cautions

In a Situation Report posted on February 1, the World Health Organization says: “WHO is aware of possible transmission of the novel coronavirus from infected people before they developed symptoms. Detailed exposure histories are being taken to better understand the pre-clinical phase of infection and how transmission may have occurred in these few instances.” It then stresses that “asymptomatic infection may be rare, and transmission from an asymptomatic person is very rare with other coronaviruses, as we have seen with Middle East Respiratory Syndrome (MERS) coronavirus. Thus, transmission from asymptomatic cases is likely not a major driver of transmission.”

The main driver of novel coronavirus transmission is people who exhibit overt symptoms. Such people will spread the virus more readily through coughing and sneezing.

The Public Health Agency of Sweden has now posted this information in the frequently asked question whether the virus infects during the incubation period. It says: “Data has circulated that the new corona virus would be [transmitted] throughout the incubation period… It has emerged that the data is unfortunately based on misconceptions. We believe that it is impossible for the new corona virus to infect throughout the incubation period.”

And about the NEJM article it says: “The sources that claimed that the coronavirus would infect during the incubation period lack scientific support for that analysis in their articles. This applies, among other things, to an article in NEJM that has subsequently proven to contain major flaws and errors. Statements by the Chinese authorities on infectiousness during the incubation period lack sources or other data to support it.”

Published in The Hindu on February 4, 2020