Transmission

Cough/Sneeze droplets visualized in dark background using Tyndall scattering
File:COVID19 in numbers- R0, the case fatality rate and why we need to flatten the curve.webm

See also: Severe acute respiratory syndrome coronavirus 2 § Infection
Respiratory droplets, produced during sneezing and coughing.

A video discussing the basic reproduction number and case fatality rate in the context of the pandemic.

Details about transmission of the disease are still being learned.[9][10] According to the World Health Organization and the United States Center for Disease Control, it is mainly spread during close contact and via respiratory droplets produced during coughing and sneezing.[10][8] Close contact is within 1 to 2 metres (3 to 6 feet).[8][10] Respiratory droplets may also be produced during breathing, specifically breathing out (exhaling), including talking, but the virus is not thought to be airborne or to spread over large distances.[8] It may also spread when one touches a contaminated surface and then their eyes, nose, or mouth.[8] While there are concerns it may spread via faeces, this risk is believed to be low.[8][10]

It is most contagious when people are symptomatic, and although spread may be possible before symptoms appear, this risk is very low.[10][8] The CDC states that the virus “seems to be spreading easily and sustainably in the community in some areas”.[10] The European Centre for Disease Prevention and Control (ECDC), as of 24 March, notes that there is not enough information about how easily and sustainably the disease spreads, but one person generally infects two to three others.[9] The virus can remain infectious for hours to days on surfaces such as door handles.[290] Specifically, the virus was found to be infectious for up to three days on plastic and stainless steel, for one day on cardboard, and for up to four hours on copper.[291] This, however, varies based on the humidity and temperature.[292] While the virus does not generally spread through the air,[8] it may survive for up to three hours in aerosol form.[291][293] An article in Wired magazine pointed out that public health authorities often use “airborne” in a specialized sense to mean highly airborne transmissible such as measles. And while COVID-19 may not meet this high level, it may still be airborne in a more limited sense.[294]

Surfaces may be decontaminated with a number of solutions (within one minute for a stainless steel surface), including 62–71% ethanol, 50–100% isopropanol, 0.1% sodium hypochlorite, 0.5% hydrogen peroxide, and 0.2–7.5% povidone-iodinebenzalkonium chloride and chlorhexidine gluconate are less effective.[295]

Virology

Main article: Severe acute respiratory syndrome coronavirus 2

Illustration of SARSr-CoV virion

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel severe acute respiratory syndrome coronavirus, first isolated from three people with pneumonia connected to the cluster of acute respiratory illness cases in Wuhan.[237] All features of the novel SARS-CoV-2 virus occur in related coronaviruses in nature.[296]

SARS-CoV-2 is closely related to the original SARS-CoV.[297] It is thought to have a zoonotic origin. Genetic analysis has revealed that the coronavirus genetically clusters with the genus Betacoronavirus, in subgenus Sarbecovirus (lineage B) together with two bat-derived strains. It is 96% identical at the whole genome level to other bat coronavirus samples (BatCov RaTG13).[280][298] In February 2020, Chinese researchers found that there is only one amino acid difference in certain parts of the genome sequences between the viruses from pangolins and those from humans, however, whole-genome comparison to date found at most 92% of genetic material shared between pangolin coronavirus and SARS-CoV-2, which is insufficient to prove pangolins to be the intermediate host.[299]