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Coronavirus: is SARS-CoV-2 contagious for significantly longer?

Health authorities are concerned about unclear infection routes and indications that the incubation period is twice as long. Longer contagion times would have drastic consequences for prevention.

The incubation period for the new virus, i.e. the time between infection and the onset of symptoms, is normally 2 to 14 days. The World Health Organization (WHO),  the German Robert Koch Institute and the Federal  Ministry of Health continue to assume this period. Accordingly, suspected cases are still isolated for two weeks.

Most often, the first symptoms appear after three days, as China’s leading epidemiologist Zhong Nan Shan, the head of the National Panel of Experts on Curbing Lung Disease, found. His team had examined 1,099 cases from 552 hospitals in China. 

However, these are preliminary results that need further investigation, said Zhong Nan Shan, who discovered the SARS coronavirus in 2003. In rare cases, the incubation period for the new coronavirus can be up to 24 days, according to the study from February 9, 2020, which was published on the medical research platform medRxiv. It says: “The median incubation period was 3.0 days (range, 0 to 24.0 days).” 

Individual cases or incorrect control?

A few days ago, a report from the provincial government of Hubei, the epicenter of the virus, caused a sensation that a 70-year-old man only showed symptoms 27 days after the infection.

However, such individual cases are only meaningful to a limited extent, according to the German coronavirus expert Christian Drosten from the Berlin Charité:  “A frequent source of error in apparently very long incubation times is an unnoticed interim exposure.”

Christian Drosten sees no reason to change the previous assessments regarding the incubation period. It can only be excluded under very controlled conditions that those affected have been exposed to the pathogen several times in succession. 

Different bodies react differently quickly

In the view of Thomas Pietschmann,  molecular virologist at Twin core, the center for experimental and clinical infection research, it is not surprising that different patients react differently to pathogens and thus the incubation times vary considerably: “Viruses have different properties, as they are in spread to a host and at the same time suppress the immune response, and such processes mean that it takes longer, or that the virus is recognized earlier and the symptoms set in, “Pietschmann said in a DW interview.

Gradually it becomes clearer that there are occasionally significantly longer incubation times, says Prof. Dr. Jonas Schmidt-Chanasit from the German Center for Infection Research.  But the vast majority of those infected showed symptoms after just a week: “You just learn something new, it has been an unknown virus so far. We have known it for two months and you now have more patients and more cases that you can understand you have more data that show that in a few cases – it must be emphasized again – the incubation period can be longer, up to over a month, but most get sick within a week, that’s the mass, and therefore we work, “Schmidt-Chanasit told Deutsche Welle.

Japan Coronavirus Covid-19 cruise ship Diamond Princess (picture-alliance / AP Photo / Yomiuri Shimbun)The crew and passengers of the Diamond Princess will remain at home for two weeks after two weeks of quarantine

What does a significantly longer incubation period mean?

However, if the incubation period of the virus is significantly longer than the expected 14 days, this could have a drastic impact on efforts to contain the epidemic. Because then the usual quarantine time of 14 days would not be sufficient.

For example, if the many Chinese workers return from their two-week forced vacation back to their factories and businesses, this could lead to the second wave of infections.

Japan’s Minister of Health Katsunobu Kato has therefore asked all passengers and crew members of the cruise ship “Diamond Princess” to stay at home for an additional two weeks after the two-week quarantine on board. 

The virus had only been detected at home in two Australians, even though they had tested negative on the “Diamond Princess”.

Not understandable ways of infection

In addition to the indications of a longer incubation period, the WHO is also concerned about the often incomprehensible routes of infection and those infections where there is no clear epidemiological connection, according to WHO Director-General Tedros Adhanom Ghebreyesus on Twitter.

According to WHO Director-General Tedros Adhanom Ghebreyesus, many people were infected with the new SARS-CoV-2 even though they were neither in China nor in contact with anyone who had been diagnosed with the coronavirus. 

This supports the now common assumption that largely or completely symptom-free people can spread the pathogen further. 

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