Fact check: Can coronavirus spread during incubation, when infected is symptom-free?

One of the major fears during the coronavirus outbreak was the possibility of the virus' potential to spread from one person to another during its incubation period, when the patient is asymptomatic. Even during the initial phases of the outbreak, Chinese researchers had suspected that could be the case, though there was no solid proof of the same. Then came a report in the New England Journal of Medicine (NEJM) in January that seemed to confirm the theory. The study dealt with a Shanghai resident, who arrived in Germany's Munich on a business trip. According to NEJM, the resident displayed no symptoms while arriving, but was taken ill on the flight back to China; it was later tested Wuhan coronavirus positive. Two people in Germany, who had come into direct contact with the Shanghai resident, contracted nCoV, which pointed to a possibility that the virus spread when the Shanghai resident was asymptomatic. "It is notable that the infection appears to have been transmitted during the incubation period of the index patient, in whom the illness was brief and nonspecific. The fact that asymptomatic persons are potential sources of 2019-nCoV infection may warrant a reassessment of transmission dynamics of the current outbreak," according to the study. 

However, the study has now come under fire, with multiple agencies pointing out the methodology was flawed. Publication Science wrote a rejoinder, citing Robert Koch Institute (RKI), the German government’s public health agency, that the Shanghai resident was not actually asymptomatic while on her visit to Germany. According to the publication: "The researchers didn’t actually speak to the woman before they published the paper. The last author, Michael Hoelscher of the Ludwig Maximilian University of Munich Medical Center, says the paper relied on information from the four other patients: "They told us that the patient from China did not appear to have any symptoms.” Afterward, however, RKI and the Health and Food Safety Authority of the state of Bavaria did talk to the Shanghai patient on the phone, and it turned out she did have symptoms while in Germany. According to people familiar with the call, she felt tired, suffered from muscle pain, and took paracetamol, a fever-lowering medication. [An RKI spokesperson would only confirm to Science that the woman had symptoms.]"

In an email to CNN on Tuesday, German public health officials said the NEJM report was incorrect. "In contrast to first reports according to which the index case [a Chinese traveling in Germany] seemed to have been asymptomatic during the time of likely transmission here, recent interviews by the Bavarian health authorities and the Robert Koch Institute in Chinese language revealed that she might have had mild unspecific symptoms including back pain and also took antipyretic medication."

Sweden's public health agency, on its website, also claimed that "they believed it is impossible for the new coronavirus to infect throughout the incubation period."

According to the agency: "Data has circulated that the new coronavirus would be infected throughout the incubation period. This information has not been presented in a way that provides scientifically substantiated facts. Rather, it has emerged that the information is unfortunately based on misconceptions. We believe it is impossible for the new corona virus to infect throughout the incubation period."

"There are solid scientific studies and a scientific evaluation on the coronavirus that causes the disease SARS. The evaluation clearly shows that the [Wuhan] coronavirus does not infect at all during the incubation period. There is therefore much to suggest that similar would also apply to the new coronavirus."

Thus, with the emergence of fresh reports, it is still not known whether the coronavirus spreads during its incubation period. 

Unknowns make the battle harder

Health authorities are scrambling to halt the spread of a new virus that has killed hundreds in China. But with important details about the illness and how it spreads still unknown, officials and medical personnel are struggling. Governments have rushed to get their citizens out of China while also restricting visitors from the country, which is orchestrating history's largest anti-viral campaign by blocking 50 million people from leaving Wuhan, the center of the outbreak, and nearby areas.  A growing number of Chinese cities are discouraging people from even leaving their apartments. Villages have blocked entry points with piles of dirt and rubble, while businesses and offices remain closed indefinitely.

As Beijing's authoritarian leadership faces questions over having kept its citizens in the dark for weeks before infections started to explode, other countries are trying to set up effective quarantines to stop a possible pandemic. Those efforts have not always been smooth, with violent protests near quarantine centers, banishment to remote islands, the confinement of thousands on a cruise ship, and some citizens allowed to leave quarantine early.

A look at the world's sometimes-wobbly efforts to stop the crisis:

South Korea has confirmed 18 cases of infection with the new type of coronavirus and there are fears of a broader local spread.

The country has banned entry to all foreigners who have traveled to China's Hubei province, where Wuhan is located, after Jan. 21. The government says it will consider stopping South Korean tourist visits to China if the outbreak worsens.

Officials have acknowledged missteps in monitoring visitors from China and in tracing the contacts of those infected.

Anxiety abounds. Movie theaters, shopping malls and restaurants have closed. A large church in Seoul skipped Sunday services because a virus patient had attended earlier. Parents have kept schoolchildren at home. Stores are running out of face masks and hand sanitizers.

Residents of central South Korea threw eggs and other objects at government officials over plans to quarantine about 700 evacuees from Wuhan at government facilities in their neighborhoods.

Australia has been criticised over its decision to quarantine about 300 Wuhan evacuees on a remote island used in the past to banish asylum seekers and convicts. Critics say a quarantine center on the Australian mainland would be preferable to Christmas Island.  Some inhabitants of the island say the government is turning their home into a leper colony. The government argues that the location strikes a balance between supporting Australians stranded in China and protecting the wider Australian population from the disease.

People on the Australian mainland who might have caught the virus are not placed in quarantine, but are advised to self-isolate for 14 days, which scientists say is the longest incubation period of the virus. The 13 confirmed cases are being treated in hospitals.

Starting this month, Australia has banned foreigners without permanent residency from entering the country if they had visited mainland China in the previous 14 days. China's national women's soccer team has been quarantined at a Brisbane hotel since arriving last week.

Japan, which has reported 33 cases, stepped up quarantine measures after officials were criticized last week for allowing two evacuees from Wuhan to leave early from a hotel where they had been quarantined.

Officials say 518 evacuees have been placed under a 14-day quarantine at a hotel and three government facilities near Tokyo. Those with symptoms have been treated in isolation rooms at hospitals.

On Tuesday, the government confirmed at least 10 cases on a cruise ship and are quarantining its 3,700 crew and passengers on board.

Starting Saturday, Japan banned the entry of foreigners who have visited Hubei province in the previous 14 days. Social media is overflowing with comments calling for a ban on all visitors from China. I'm afraid Japan will be soon criticized for taking less measures than other countries, said Mitsunori Okamoto, an opposition lawmaker.

North Korea has yet to report a case, but it's still pushing a tough campaign to prevent the spread of the virus, which state media have called a matter of national existence.  The country has blocked tourists, reduced flights and strengthened screening at borders, harbors and airports. State media say 30,000 health workers have been mobilized across the country for preventive measures. Rival South Korea last week withdrew dozens of officials from an inter-Korean liaison office in Kaesong after North Korea insisted on closing it until the epidemic is controlled. Because fighting the virus is crucial for defending the security of the country and the life and safety of people, all the workers in the anti-epidemic field set up rapid reaction teams ... so as to promptly counter any slightest situation, Pyongyang's official Rodong Sinmun newspaper said.

March Air Reserve Base in California's Riverside County is near capacity after housing 195 people flown in from Wuhan who are now under a federal quarantine. We're pretty much full at this point, said Maj. Perry Covington, a spokesman at the base.

None of the evacuees at the base has shown signs of the illness.

Tents were set up over the weekend to assist in screening passengers in case other U.S.-bound flights from Wuhan are diverted to the base due to weather or other reasons. 

-Inputs from agencies