Cases of Covid-19 first emerged in late 2019, when a mysterious illness was reported in Wuhan, China. The cause of the disease was soon confirmed as a new kind of coronavirus, and the infection has since spread to many countries around the world and become a pandemic.
On 11 February the World Health Organization announced that the official name would be covid-19, a shortened version of coronavirus disease 2019. The WHO refers to the specific virus that causes this disease as the covid-19 virus.
This is not the formal name for the virus – the International Committee on Taxonomy of Viruses calls it the “severe acute respiratory syndrome coronavirus 2”, or SARS-CoV-2, because it is related to the virus that caused the SARS outbreak in 2003. However, to avoid confusion with SARS the WHO calls it the covid-19 virus when communicating with the public.
Early in the outbreak, the virus was called 2019-nCoV by the WHO. The virus is also often referred to as the novel coronavirus, 2019 coronavirus or just the coronavirus.
The WHO’s definition of a confirmed case of covid-19 is a person shown by laboratory testing to be infected with the virus, irrespective of clinical signs and symptoms. However, some reported case numbers from China have included people with symptoms of covid-19, but without laboratory confirmation.
The most commonly reported symptoms include a fever, dry cough and tiredness, and in mild cases people may get just a runny nose or a sore throat. In the most severe cases, people with the virus can develop difficulty breathing, and may ultimately experience organ failure. Some cases are fatal.
The virus can also be asymptomatic, causing no noticeable illness in some people – but these people are still contagious and can spread the virus.
On 11 March, the WHO announced that the outbreak should be considered a pandemic – a term that has no universally agreed definition, but means that multiple countries are seeing sustained transmission between people of an outbreak causing disease or death.
Calculating fatality rates
The risk of death has been difficult to calculate, as it relies on accurate numbers of those who have symptoms but survive – and some countries, including the US, have been slow to increase capacity for testing. A small study of people who contracted covid-19 in Wuhan suggests that the risk of death increases with age, and is also higher for those who have diabetes, disease, blood clotting problems, or have shown signs of sepsis.
Children, on the other hand, seem to be less likely to get severely ill and die from the new coronavirus, possibly due to less developed immune responses. Pregnant people don’t seem to be at greater risk of experiencing severe covid-19 than other adults, and it doesn’t seem to pass on to fetuses, but further, larger studies are needed to confirm this.
Young, healthy adults are still at risk of contracting covid-19 and developing severe, life-threatening disease.
The spread of covid-19
Covid-19 is a respiratory illness and is largely spread via droplets in the air. These are typically expelled when an infected person coughs or sneezes.
Once symptoms develop, a person’s viral load declines steadily, and they become increasingly less infectious. However, people appear to keep shedding the virus for around two weeks after they recover from covid-19, both in their saliva and stools. This means that even once a person’s symptoms have cleared, it may still be possible to infect other people.
People with mild or no symptoms can have a very high viral load in their upper respiratory tracts, meaning they can shed the virus through spitting, touching their mouths or noses and then a surface, or possibly talking. The new coronavirus has also been found to persist for days on surfaces, though that doesn’t necessarily mean these virus particles could still infect other people. That could be diminished by ultraviolet light, heat or humidity.