Questions and answers on COVID-19: Basic facts
1. What is SARS-CoV-2? What is COVID-19?
Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is the name given to the 2019 novel coronavirus. COVID-19 is the name given to the disease associated with the virus. SARS-CoV-2 is a new strain of coronavirus that has not been previously identified in humans.
2. Where do coronaviruses come from?
Coronaviruses are viruses that circulate among animals. Some coronaviruses can infect humans.
Bats are considered natural hosts of these viruses, and several other species of animals are also known to act as sources. For instance, Middle East Respiratory Syndrome Coronavirus (MERS-CoV) is transmitted to humans from camels, while Severe Acute Respiratory Syndrome Coronavirus-1 (SARS-CoV-1) is transmitted to humans from intermediate hosts such as civet cats which played a role in the emergence of SARS-CoV-1.
3. Is this virus comparable with SARS or with the seasonal flu?
The novel coronavirus detected in China in 2019 is closely related genetically to the SARS-CoV-1 virus. SARS emerged in late 2002 in China and caused more than 8 000 cases in 33 countries over the course of eight months. Around one in 10 people who developed SARS died.
In the first eleven months of the COVID-19 pandemic (from 31 December 2019 to 14 December 2020), there were over 71 million cases worldwide and more than 1 600 000 deaths.
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While the viruses that cause both COVID-19 and seasonal influenza are transmitted from person-to-person in the same way and may cause similar symptoms, the two viruses are different.
ECDC estimates that between 15 000 and 75 000 people die prematurely every year in the European Union (EU), the United Kingdom (UK), Norway, Iceland and Liechtenstein due to causes associated with seasonal influenza infection. This represents approximately one in every 1 000 people who are infected. As so many people contract seasonal influenza each year, the virus results in a large number of deaths, despite its relatively low mortality rate. Evidence is still emerging from around the world with relation to the associated mortality for COVID-19, but to date, data suggest that COVID-19 has a higher proportion of cases with severe infection and a higher mortality than seasonal influenza. Some people who have had COVID-19 experience long-term effects, with ongoing respiratory and neurological symptoms. COVID-19 appears to be more transmissible than seasonal influenza, with one infected individual leading to a higher number of secondary infections than is the case for influenza. As SARS-CoV-2 is a new virus, there was no prior immunity, so the entire human population was susceptible to SARS-CoV-2 infection at the start of the pandemic and until very recently there was no vaccine available.
4. How does the virus spread?
SARS-CoV2 is mainly transmitted via respiratory droplets and aerosols from an infected person when they sneeze, cough, speak or breathe and are in close proximity to other people. The virus has also been isolated from the faeces of infected cases, indicating that faecal-oral transmission might also be a route of infection. Droplets can be inhaled or can land on surfaces that others come into contact with and are then infected when they touch their nose, mouth or eyes. The virus can survive on surfaces from anything between a few hours (copper, cardboard) to a number of days (plastic and stainless steel). However, the amount of viable virus declines over time and it may not always be present in sufficient quantities to cause infection.
The incubation period for COVID-19 (i.e. the time between exposure to the virus and the onset of symptoms) is currently estimated to be between one and 14 days.
We know that the virus can be transmitted when people who are infected show symptoms such as coughing. A person who is infected can also transmit the virus up to two days before they show symptoms; the extent to which such asymptomatic infections contribute to the overall transmission is not currently clear.
5. When is a person infectious?
The infectious period may begin around two days before symptoms appear, but people are most infectious during the symptomatic period, even if symptoms are mild and non-specific. The infectious period is estimated to last for eight to 10 days in moderate cases, and up to two weeks on average in severe cases.
6. How severe is COVID-19 infection?
Data from the EU/European Economic Area (from those countries with available data) show that up to 30% of diagnosed COVID-19 cases are hospitalised, depending heavily on age, and up to 20% of those hospitalised need ventilatory support. It is important to note, however, that people with more severe symptoms are more likely to be tested than those with less severe symptoms. The actual proportion of people requiring hospital admission from the overall number of infected individuals is therefore lower than these figures suggest. Hospitalisation rates are higher for those aged 60 years and above, and for those with underlying health conditions.