Yang Y, Shang W, Rao X. Facing the COVID‐19 outbreak: What should we know and what could we do? J Med Virol. 2020;1--2. 10.1002/jmv.25720 31502247

An outbreak of a novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), emerged in late December 2019 in Wuhan City, Hubei Province in China and caused atypical pneumonia called coronavirus disease 2019 (COVID‐19).[^1^](#jmv25720-bib-0001){ref-type="ref"} The disease is characterized by fever, cough, fatigue, and ground‐glass opacity on chest tomography.[^1^](#jmv25720-bib-0001){ref-type="ref"}, [^2^](#jmv25720-bib-0002){ref-type="ref"} The epidemic began with four confirmed cases on 29 December 2019.[^2^](#jmv25720-bib-0002){ref-type="ref"} The first confirmed case in Tibet was announced 1 month later on 29 January 2020. SARS‐CoV‐2 had swept the entire of China, including Hong Kong, Macao, and Taiwan, in only 1 month. A total of 72 528 laboratory‐confirmed cases and 1870 deaths have been reported in China as of 18 February 2020,[^3^](#jmv25720-bib-0003){ref-type="ref"} and 25 countries outside China have reported confirmed cases.[^3^](#jmv25720-bib-0003){ref-type="ref"} The WHO issued a public health emergency of international concern on 30 January 2020.

How could SARS‐CoV‐2 spread so fast?

In general, the emergence of an infectious disease consists of three vital elements: infectious source, susceptible population, and transmission route. The source of SARS‐CoV‐2 is complex. Most patients with COVID‐19 among the first cluster of pneumonia cases (27 of 41, 65.9%) were exposed to Huanan seafood market,[^2^](#jmv25720-bib-0002){ref-type="ref"} and several wild animals, including bats, snakes, minks, and pangolins, were reported to be the possible reservoir for SARS‐CoV‐2.[^4^](#jmv25720-bib-0004){ref-type="ref"}, [^5^](#jmv25720-bib-0005){ref-type="ref"}, [^6^](#jmv25720-bib-0006){ref-type="ref"} Patients are currently the major sources for the COVID‐19 outbreak given the increasing number of cases. Mild but infectious cases may also serve as sources and make COVID‐19 difficult to control.[^7^](#jmv25720-bib-0007){ref-type="ref"}

As the causative agent of COVID‐19, SARS‐CoV‐2 was quickly isolated and its whole genome sequence was submitted to GenBank (accession number MN908947) on 5 January 2020.[^8^](#jmv25720-bib-0008){ref-type="ref"} Bioinformatic analyses have shown that SARS‐CoV‐2 belongs to the genus of β‐coronavirus and shares at least 70% similarity in genetic sequence with SARS‐CoV, another kind of β‐genus CoV that caused a large‐scale coronavirus infection in China in 2002.[^6^](#jmv25720-bib-0006){ref-type="ref"} Additionally, SARS‐CoV‐2 and SARS‐CoV may recognize the same receptor, the angiotensin‐converting enzyme 2 (ACE2).[^6^](#jmv25720-bib-0006){ref-type="ref"} One important difference is that several key residues on the spike (S) protein of SARS‐CoV‐2 have changed when compared with SARS‐CoV.[^5^](#jmv25720-bib-0005){ref-type="ref"} Wan et al[^5^](#jmv25720-bib-0005){ref-type="ref"} suggested that these mutations may weaken virus‐receptor interactions. Nevertheless, the latest reports argued that SARS‐CoV‐2 S protein binds ACE2 with a much higher affinity than SARS‐CoV S protein does.[^9^](#jmv25720-bib-0009){ref-type="ref"} This may be an important factor contributing to the quick spread of COVID‐19.

A susceptible population is the second important factor for COVID‐19 control. Several groups have analyzed the clinical features of SARS‐CoV‐2‐infected patients to elucidate what factors considerably influenced disease outcomes.[^1^](#jmv25720-bib-0001){ref-type="ref"}, [^2^](#jmv25720-bib-0002){ref-type="ref"} Li et al[^2^](#jmv25720-bib-0002){ref-type="ref"} showed that, among the 425 patients who were confirmed before 22 January 2020, elderly patients were more likely to suffer severe infections, and no child (\<15‐years old) were infected. However, age may have little relationship with SARS‐CoV‐2 infection, and all individuals have an equal possibility of being infected because of the increasing number of cases.[^1^](#jmv25720-bib-0001){ref-type="ref"} The high‐risk population are those who have an exposure history, are older, and have underlying diseases, such as hypertension and chronic obstructive pulmonary disease.[^1^](#jmv25720-bib-0001){ref-type="ref"}

The route of transmission is the third important factor for infectious disease. SARS‐CoV‐2 is transmitted between humans mainly via aerial droplets and direct contact.[^1^](#jmv25720-bib-0001){ref-type="ref"}, [^2^](#jmv25720-bib-0002){ref-type="ref"} The virus is also found in stool specimens of patients, suggesting potential fecal‐oral transmission pathway; however, this route requires further investigation.[^10^](#jmv25720-bib-0010){ref-type="ref"} The Wuhan government has pronounced to shut down public transport system since 23 January 2020 to control virus transmission. All other cities in Hubei Province implemented similar policies in the next 3 days. However, SARS‐CoV‐2 transmission seemed to be not effectively controlled. Only 425 cases were reported before 22 January 2020, yet, the confirmed cases have explosively increased since then.[^2^](#jmv25720-bib-0002){ref-type="ref"}, [^3^](#jmv25720-bib-0003){ref-type="ref"} One possible reason may be that millions of people had left Wuhan for the traditional Spring Festival before the city closed. If any of these people were infected, they would be dangerous sources of the following generations of virus transmission. Community transmission has been ongoing in a number of provinces outside the Hubei Province in China. Guangdong, Henan, Zhejiang, Hunan, Anhui, and Jiangxi provinces have all announced a huge number of confirmed cases (more than 900).[^3^](#jmv25720-bib-0003){ref-type="ref"} Local transmission chains in these provinces may have started through the index cases imported from Hubei Province. Their richer economic environment (Guangdong and Zhejiang) and proximity to Hubei (Henan, Hunan, Anhui, and Jiangxi) mean frequent population exchanges and, consequently, frequent virus transmission.

Thus far, no proven and specific antiviral treatments for COVID‐19 are available.[^7^](#jmv25720-bib-0007){ref-type="ref"} Thus, what could we do to fight COVID‐19? The most important goal is to control infectious sources. The Chinese government rapidly initiated serial measures, such as isolating Wuhan and then the whole Hubei Province, improving epidemic information monitoring and reporting, and detecting, isolating, and curing patients. More than 8000 physicians and nurses from other provinces went to Hubei Province and started to combat the disease with local medical staff.[^7^](#jmv25720-bib-0007){ref-type="ref"} At the same time, two hospitals with 2600 beds in total have been built in Wuhan for confirmed and suspected patients.[^7^](#jmv25720-bib-0007){ref-type="ref"} A fast and effective detection system was established and maintained to differentiate suspected patients continuously. Rational supervision on wild vectors may also be important but is easily ignored. The second thing we could do is to safeguard susceptible people. The Chinese government has quickly organized supplies and taken measures based on SARS‐CoV epidemic control to guarantee the order of daily life. Popular science propaganda was widely implemented to evoke civilians with self‐protection and hand hygiene and to reduce going out. Third, authorities need to take measures to cut off the transmission of SARS‐CoV‐2 among local residents. For example, the Chinese Spring Festival holidays should be extended and school openings should be postponed. Besides, home quarantine is the best choice for residents, however, the widespread lockdown may inevitably bring a psychological effect; hence, mental health counseling and popularization are recommended. Lastly, we should say that what we have done today is not only to control COVID‐19 but, more importantly, to build a security system to prevent similar outbreaks in the future.
