The outbreak of novel coronavirus pneumonia (named COVID-19) in the world began in December 2019, the pathogen that causes COVID-19 to be listed as a global pandemic is a new type of coronavirus (Burke and Fang, 2020) . In February 11, 2020, the International Committee on Virus Classification officially named the virus as Severe Acute Respiratory Syndrome Coronavirus 2, referred to as "SARS-CoV-2" (Gorbalenya et al., 2020).

So far, SARS-CoV-2 has been prevalent in more than 216 countries as of May 28, 2020 (last update: 28 May 2020, 17:00 GMT-7). There are about 5,704,736 confirmed infections in the world, including more than 357,736 deaths. The numbers are still rising rapidly (https://www.who.int/emergencies/diseases/novel-coronavirus-2019).

SARS-CoV-2 is a positive-sense single-stranded RNA virus. It is a strain of severe acute respiratory syndrome-related coronavirus (SARSr-CoV), belonging to the genus Betacoronavirus in the family of Coronaviridae. Its gene sequence belongs to the same genealogy but different evolutionary clades as SARS virus and MERS virus. It is the seventh known coronavirus that can infect humans.

SARS-CoV-2 can invade the human body through the upper respiratory tract. The ACE2 expressed on the surface of various cells is used as the receptor to infect the human body. The main infected organs include lungs, heart, kidneys and other major organs (Zhou et al., 2020; Yang et al., 2020).

SARS-CoV-2 has become a kind of super virus in human history due to its typical characteristics, such as super infectivity, long average incubation period, low mortality, etc.

1 Three Basic Characteristics of Super Virus

1.1 Strong infectivity

After any virus infects the host cell, it will choose the direction of higher infectivity for mutation. Infectivity is a measure of how easy it is for a virus to find a host cell, which usually expressed as the Basic reproduction number, and denoted R0. According to the existing research, the R0 of SARS-CoV-2 virus is between 3.11-6.47 (Read et al., 2020; Tang et al., 2020; Zhao et al., 2020), which is much higher than that of SARS in the same genus, in which the R0 coefficient is about 3( https://www.who.int/csr/sars/en/WHOconsensus.pdf ).

Before the lockdown of Wuhan in China, some scholars thought that the R0 of Wuhan was 5.0, while the research team led by Tang Biao of Xi'an Jiaotong University published an article on January 24, 2020 that the R0 might be as high as 6.47 (Tang et al., 2020).

Since the outbreak of SARS-CoV-2 in China, it has been under the control of doctors, hospitals, and disease control institutions (Luo and Mason, 2020), especially after the lockdown of Wuhan City. With the improvement of prevention schemes such as urban blockade, community closure, and isolation at home, all factors have a great impact on the epidemic dynamics model. The number of people infected increased slowly before the peak. The numbers did not increase exponentially (Huang and Qiao, 2020). The R0 factor should be around 3.

On the contrary, for the UK and other countries that advocate "herd immunity", as well as the United States that adopt moderate "stay at home" and "social distancing", the R0 coefficient is relatively high. It is speculated that the R0 coefficient of European and American countries should be more than 5.

1.2 Long incubation period

The length of incubation period is a measure of the adaptability of virus to host cells. It is an evolution of the virus itself that the virus that has found the host cell to be "Lurked" and colonized (settle down and reproduce) for a long time. The known incubation period for HIV can be as long as 10 years.

Some studies have pointed out that the average incubation period of SARS-CoV-2 virus is 5.2 days. On February 9, 2020, the team led by Zhong Nanshan, famous Chinese doctor, published a new comprehensive study, extending the upper limit of the incubation period to 24 days. During the development of the epidemic, a large number of asymptomatic SARS-CoV-2 carriers appeared, and they have the potential of recessive transmission. Based on the analysis of 30000 cases in Hubei Province of China, it is believed that 30-60% of those infected with the virus will become asymptomatic or only slightly symptomatic virus carriers (Qiu, 2020). Later studies further found that asymptomatic and mild SARS-CoV-2 carriers were not inferior to symptomatic patients in transmission ability, and the incubation period of second and third generation virus carriers was longer on average.

1.3 Low mortality

Mortality is a measure of the ability of the virus to survive. If the virus enters the host cell and kills the host immediately, the virus itself will also die. After SARS-CoV-2 entered the human body, it caused COVID-19 pneumonia. Compared with 9% mortality rate of SARS and 36% mortality rate of MERS, the mortality rate of SARS-CoV-2 was very low, ranging from 0.1% to 1.6%.

According to clinical data, the shortest time from the onset of symptoms to death is two weeks, and the longest time is up to eight weeks. The overall mortality rate of patients under 50 years old is less than 0.5%, while that of the elderly over 70 years old is more than 8% (Castagnoli et al., 2020).

The total clinical mortality rate in mainland China was 0.66%, with a 95% confidence interval of 0.39~1.3 (Verity et al., 2020). In the United States, the clinical mortality rate under 55 years old is less than 0.8% (CDC Covid-19 Response Team, 2020).

2 Diversity of Host Cells

No virus can survive without its host cell. Therefore, the virus should strive to evolve or mutate to find suitable host cells. The variety of host cells that can be parasitized is conducive to the survival of the virus itself. Smallpox virus is eliminated by human because of the single host cell.

In addition to human beings, the host of SARS-CoV-2 can be a variety of animals, such as mice, ferrets, hamsters, etc., which are used to construct infection models (Kim et al., 2020). In addition, the two closest "peoples friend", cats and dogs, have been confirmed to be the hosts of SARS-CoV-2 (Med, 2020; Sia et al., 2020; Sit et al., 2020).

According to a paper published on the international academic platform by Professor Shi Zhengli of Wuhan Institute of Virology, Chinese Academy of Sciences, they sampled 102 cats during the epidemic in Wuhan, and 14.7% of them were infected with SARS-CoV-2 (Zhang et al., 2020).

A team experiment led by virologist Dr. Zhigao Bu showed that infected cats can transmit SARS-CoV-2 through air (Shi et al., 2020).

The Malik Peiris team of the University of Hong Kong published a research paper entitled "infection of dogs with sars-cov-2" online in Nature. The research used quantitative RT-PCR, serology, virus genome sequencing, and virus isolation from a dog. It was found that 2 of 15 dogs in Hong Kong were infected by SARS-CoV-2 (Sit et al., 2020).

It has also been reported that humans have transmitted SARS-CoV-2 to pet cats. On March 27, 2020, Belgium reported the first known case of pet cat infection. A confirmed COVID-19 patient in Hong Kong infected his pet dog with SARS-CoV-2. However, studies have shown that SARS-CoV-2 is a low-level infection with poor replication ability in dogs (Shi et al., 2020).

3 Short Duration of Immunity

The innate immune system of human body can recognize SARS-CoV-2 successfully and produce specific antibody, which makes the infected person obtain immunity. The duration of immunity is closely related to the survival time and prevalence of the virus itself. After humans being infected with smallpox virus, they can obtain permanent immunity, which leads to the extinction of smallpox virus by vaccination. The duration of immunity will directly affect the frequency of SARS-CoV-2 outbreak in the future.

The duration of human immunity to SARS-CoV-2 is short. Clinical observation shows that some patients are in line with the discharge indicators, i.e. no clinical symptoms, PCR negative standard, after several days of follow-up isolation, the result of PCR again is positive. It has been reported that patients who are cured still have the ability to transmit the virus (Lan et al., 2020). Some researchers found that SARS-CoV-2 remains in lung tissue even though some patients pass the PCR test, suggesting that discharged patients have potential risk of virus transmission (Yao et al., 2020). It shows that SARS-CoV-2 infected people have not established an effective immune defense system and ability.

The duration of human immunity to SARS-CoV-2 is only about 40 weeks, which means that SARS-CoV-2 will be the same as other existing human viruses, such as influenza virus, which has existed in human society for a long time, and will continue to break out. The duration of immunity is far shorter than the development cycle of vaccine. The general development cycle of vaccine is at least 72 to 104 weeks.

4 Diversity of Media and Paths

As we all know, HIV transmission media are mainly body fluids, such as blood, semen, prostate fluid, vaginal secretion, human milk or wound secretion, especially semen and blood. The main routes of transmission are unsafe sexual behavior, intravenous injection, blood transfusion, delivery, lactation and so on. However, in saliva, tears, urine, feces and other samples from SARS-CoV-2 carriers, infectious pathogens have been found (Xia et al., 2020); http://med.china.com.cn/content/pid/157492/tid/1022 )。

It has also been reported that the virus has been detected on the surface of some objects and in the air in the isolation area( https://www.cdc.gov/coronavirus/2019-ncov/index.html ). SARS-CoV-2 can be transmitted through respiratory droplets, aerosol forming aerogels, skin contact, or direct contact with viral secretions. It can enter the body from the eyes, nose, and mouth (Lu et al., 2020; Van Doremalen et al., 2020).

In addition to sneezing, coughing and other ways to produce large virus particles for transmission, SARS-CoV-2 can also be atomized by other ways to infect people (Anfinrud et al., 2020); for example, whenCOVID-19 patients are intubated or operated, they will expel the virus and make it stay in the air to spread the virus in the hospital environment (Jiang et al., 2020; Lu et al., 2020; Van Doremalen et al., 2020). It is found that in a closed space, breathing and speaking alone can produce aerosol with smaller diameter. This finding suggests that virus particles can enter the lung more easily and directly infect the cells in the lung (https://www.cdc.gov/coronavirus/2019-ncov/index.html)。

To sum up, SARS-CoV-2 virus has a variety of transmission media and ways, which makes SARS-CoV-2 to have the characteristics of omnipotence and higher transmission and infection risk compared with HIV virus.

5 The Transmission Ability Little Affected by the Seasons and Climate

HIV is highly unstable in vitro. Compared with HIV, SARS-CoV-2 can survive for up to 9 days at room temperature. The virus can continue to propagate in the normal environment of 60°C, and the complete inactivation can be achieved by putting the virus in the environment of 92°C for 15 min (Pastorino et al., 2020). SARS-CoV-2 particles can survive in the air and on the surface of objects for a long time, and the virus can remain infectious on the surface of different materials for up to 2 hours to 9 days (Liu et al., 2020; Kampf et al., 2020). According to the existing cognition, the virus is heat sensitive, but it still needs 30 minutes to be exposed to ultraviolet or 56°C high temperature environment to achieve the inactivation effect( https://www.sciencedirect.com/science/article/pii/S0195670120300463 )。

Since the outbreak of Covid-19 at the end of December 2019, politicians and scholars in some western countries have hoped that SARS-CoV-2 will die out naturally with the change of seasons and the increase of temperature. However, it has been proved that the spread of SARS-CoV-2 has not disappeared because of the change of seasons and the increase of temperature. In different regions of the world, from the tropical area near the equator to the north temperate zone, SARS-CoV-2 is still active until June. We have reasons to believe that the transmission ability of the SARS-CoV-2 virus is less affected by seasons and climate, and can spread at any time of the year. It is a non-seasonal virus.

6 Conclusion

SARS-CoV-2, which causes a global pandemic, is a more of a typical virus than SARS and MERS, as well as Ebola and HIV. SARS-CoV-2 virus has five obvious characteristics: 1. Strong infectivity, long incubation period and low mortality rate; 2. Diversified host cells; 3. Short duration of immunity; 4. Complex transmission media and routes; 5. Seasons and climate have little effects on the survival and transmission ability of the virus. These five characteristics make SARS-CoV-2 virus easier to survive, spread, and adapt to the environment and climate. Once it parasitizes on a variety of host cells, it will become a "lingering" and long-term "epidemic virus". Therefore, SARS-CoV-2 virus is a type of super virus, which will bring long-term problems and challenges to human beings.

Reference

Anfinrud P., Stadnytskyi V., Bax C.E., and Bax A., 2020, Visualizing speech-generated oral fluid droplets with laser light scattering, New England Journal of Medicine

https://doi.org/10.1056/NEJMc2007800

PMid:32294341 PMCid:PMC7179962

Burke F., and Fang J., 2020, Super virus:SARS-CoV-2 caused the COVID-19 global pandemic, Biological Evidences, 10(1):1-2

Castagnoli R., Votto M., Licari A., Brambilla I., Bruno R., Perlini S., Rovida F., Baldanti F., and Marseglia G.L., 2020, Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in children and adolescents: a systematic review, JAMA

https://doi.org/10.1001/jamapediatrics.2020.1467

PMid:32320004

CDC COVID-19 Response Team, 2020, Severe outcomes among patients with coronavirus disease 2019 (COVID-19)-- united states, February 12 - March 16, 2020, Morbidity and Mortality Weekly Report (Centers for Disease Control), 69(12): 343-346

https://doi.org/10.15585/mmwr.mm6912e2

PMid:32214079

Gorbalenya A.E., Baker S.C., Baric R.S., Baric R.S., de Groot R.J., Drosten C., Gulyaeva A.A., Haagmans B.L., Lauber C., Leontovich A.M., Neuman B.W., Penzar D., Perlman S., Poon L.L.M., Samborskiy D., Sidorov I.A., Sola I., and Ziebuhr J., 2020, The species severe acute respiratory syndrome-related coronavirus: classifying 2019-nCoV and naming it SARS-CoV-2, Nature Microbiology, 5(4): 536-544

Huang N.E., and Qiao, F.L., 2020, A data driven time-dependent transmission rate for tracking an epidemic: a case study of 2019-nCoV, Science Bulletin

https://doi.org/10.1016/j.scib.2020.02.005

PMid:32288968 PMCid:PMC7128746

Jiang Y.F., Wang H.F., Chen Y.K., He J.X., Chen L.G., Liu Y., Hu X.Y., Li A., Liu S., Zhang P., Zou H.Y., and Hua S.C., 2020, Clinical data on hospital environmental hygiene monitoring and medical staffs protection during the coronavirus disease 2019 outbreak, medRxiv

https://doi.org/10.1101/2020.02.25.20028043

Kampf G., Todt D., Pfaender S., and Steinmann E., 2020, Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents, Journal of Hospital Infection

https://doi.org/10.1016/j.jhin.2020.01.022

PMid:32035997 PMCid:PMC7132493

Kim Y., Kim S.G., Kim S.M., Kim E.H., Park S.J., Yu K.M., Chang J.H., Kim E.J., Lee S., Casel M.A.B., Um J., Song M.S., Jeong H.W., Lai V.D., Kim Y., Chin B.Sik., Park J.S., Chung K.H., Foo S.S., Poo H., Mo I.P., Lee O.J., Webby R.J., Jung J.U., and Choi Y.K., 2020, Infection and rapid transmission of SARS-CoV-2 in ferrets, Cell Host & Microbe

Lan L., Xu D., Ye G.M., Xia C., Wang S.K., Li Y.R., and Xu H.B., 2020, Positive RT-PCR test results in patients recovered from COVID-19, JAMA

https://doi.org/10.1001/jama.2020.2783

PMid:32105304 PMCid:PMC7047852

Liu Y., Ning Z., Chen Y., Guo M., Liu Y., Gali N.K., Sun L., Duan Y., Cai J., Westerdahl D., Liu X.J., Ho K.F., Kan H.D., Fu Q.Y., and Lan K., 2020, Aerodynamic characteristics and rna concentration of SARS-CoV-2 aerosol in wuhan hospitals during COVID-19 outbreak, bioRxiv

https://doi.org/10.1101/2020.03.08.982637

Lu C.W., Liu X.F., and Jia Z.F., 2020, 2019-nCoV transmission through the ocular surface must not be ignored, The Lancet, 395(10224)

https://doi.org/10.1016/S0140-6736(20)30313-5

Luo J., and Mason J., 2020, COVID-19 has been under the effective control from the outbreak to the global pandemic, International Journal of Clinical Case Reports, 10(1): 1-13

Med P., 2020, Dogs caught coronavirus from their owners, genetic analysis suggests, Nature, doi: 10.1038/d41586-020-01430-5

https://doi.org/10.1038/d41586-020-01430-5

Pastorino B., Touret F., Gilles M., Lamballerie X.D., Charrel R.N., 2020, Evaluation of heating and chemical protocols for inactivating SARS-CoV-2, bioRxiv

https://doi.org/10.1101/2020.04.11.036855

Qiu J., 2020, Covert coronavirus infections could be seeding new outbreaks, Nature

https://doi.org/10.1038/d41586-020-00822-x

Read J.M., Bridgen J.R.E., Cummings D.A.T., Ho A., and Jewell C.P., Novel coronavirus 2019-nCoV: early estimation of epidemiological parameters and epidemic predictions, medRxiv

https://doi.org/10.1101/2020.01.23.20018549

Shi J.Z., Wen Z.Y., Zhong G.X., Yang L.H., Wang C., Liu R.Q., He X.J., Shuai L., Sun Z.R., Zhao Y.B., Liang L.B., Cui P.F., Wang J.L., Zhang X.F., Guan Y.T., Chen H.L., and Bu Z.G., 2020, Susceptibility of ferrets, cats, dogs, and different domestic animals to SARS-coronavirus-2, BioRxiv

https://doi.org/10.1101/2020.03.30.015347

Sia S.F., Yan L.M., Chin A.W.H., Fung K., Choy K.T., Wong A.Y.L., Kaewpreedee P., Perera R.A.P.M., Poon L.L.M., Nicholls J.M., Peiris M., and Yen H.L., 2020, Pathogenesis and transmission of SARS-CoV-2 in golden hamsters, Nature

https://doi.org/10.1038/s41586-020-2342-5

PMid:32408338

Sit T.H.C., Brackman C.J., Ip S.M., Tam K.W.S., Law P.Y.T., To E.M.W., Yu V.Y.T., Sims L.D., Tsang D.N.C., Chu D.K.W., Perera R.A.P.M., Poon L.L.M., and Peiris M., 2020, Infection of dogs with SARS-CoV-2, Nature

https://doi.org/10.1038/s41586-020-2334-5

PMid:32408337

Tang B., Wang X., Li Q., Bragazzi N.L., Tang S.Y., Xiao Y.N., and Wu J.H., 2020, Estimation of the transmission risk of the 2019-nCoV and its implication for public health interventions, Journal of Clinical Medicine, 9(2): 462

https://doi.org/10.2139/ssrn.3525558

Van Doremalen N., Bushmaker T., Morris D.H., Holbrook M., Gamble A., Williamson B.N., Tamin A., Harcourt J.L., Thornburg N.J., Gerber S.I., Lloydsmith J.O., Wit E.D., and Munster V.J., 2020, Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1, The New England Journal of Medicine

https://doi.org/10.1056/NEJMc2004973

PMid:32182409 PMCid:PMC7121658

Verity R., Okell L.C., Dorigatti I., Winskill P., Whittaker C., Imai N., Cuomo-Dannenburg G., Thompson H., Walker P.G.T., Fu H., and Dighe A., 2020, Estimates of the severity of coronavirus disease 2019: a model-based analysis, The Lancet Infectious Diseases

https://doi.org/10.1016/S1473-3099(20)30243-7

Xia J.H., Tong J.P., Liu M.Y., Shen Y., and Guo D.Y., 2020, Evaluation of coronavirus in tears and conjunctival secretions of patients with SARS-CoV-2 infection, Journal of Medical Virology

https://doi.org/10.1002/jmv.25725

PMid:32100876 PMCid:PMC7228294

Yang X.B., Yu Y., Xu J.Q., Shu H.Q., Xia J.A., Liu H., Wu Y.R., Zhang L., Yu Z., Fang M.H., Yu T., Wang Y.X., Pan S.W., Zou X.J., Yuan S.Y., and Shang Y., 2020, Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study, The Lancet Respiratory Medicine, 8(5): 475-481

https://doi.org/10.1016/S2213-2600(20)30079-5

Yao X.H., He Z.C., Li T.Y., Zhang H.R., Wang Y., Mou H.M., Guo Q.N., Yu S.C., Ding Y.Q., Liu X.D., Ping Y.F., and Bian X.W., 2020, Pathological evidence for residual SARS-CoV-2 in pulmonary tissues of a ready-for-discharge patient, Cell Research

https://doi.org/10.1038/s41422-020-0318-5

PMid:32346074 PMCid:PMC7186763

Zhang Q., Zhang H.J., Huang K., Yang Y., Hui X.F., Gao J.D., He X.L., Li C.F., Gong W.X., Zhang Y.F., Peng C., Gao X.X., Chen H.C., Zou Z., Shi Z.L., and Jin M., 2020, SARS-CoV-2 neutralizing serum antibodies in cats: a serological investigation, bioRxiv

https://doi.org/10.1101/2020.04.01.021196

Zhao S., Lin Q.Y., Ran J.J., Musa S.S., Yang G.P., Wang W.M., Lou Y.J., Gao D.Z., Yang L., He D.H., and Wang M.H., 2020, Preliminary estimation of the basic reproduction number of novel coronavirus (2019-nCoV) in China, from 2019 to 2020: A data-driven analysis in the early phase of the outbreak, International Journal of Infectious Diseases, 92: 214-217

https://doi.org/10.1016/j.ijid.2020.01.050

PMid:32007643 PMCid:PMC7110798

Zhou P., Yang X.L., Wang X.G., Hu B., Zhang L., Zhang W., Si H.R., Zhu Y., Li B., Huang C.L., Chen H.D., Chen J., Luo Y., Guo H., Jiang R.D., Liu M.Q., Chen Y., Shen X.R., Wang X., Zheng X.S., Zhao K., Chen Q.J., Deng F., Liu L.L., Yan B., Zhan F.X., Wang Y.Y., Xiao G.F., and Shi Z.L., 2020, Discovery of a novel coronavirus associated with the recent pneumonia outbreak in humans and its potential bat origin, bioRxiv

https://doi.org/10.1101/2020.01.22.914952