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 novel coronavirus which first appeared in Wuhan, China, in 2019. SARS-CoV-2 is a new strain of coronavirus which had not been identified in humans before. Coronavirus disease 2019 (COVID-19) is the respiratory illness caused by SARS-CoV-2.

2. Where do coronaviruses come from?

Coronaviruses are viruses that circulate among animals. Some coronaviruses can infect humans.

Many human coronaviruses come from bats which are considered natural hosts of these viruses. The virus is then thought to be passed on through an intermediate host to humans. The first SARS-CoV originated in bats and was transmitted to humans via civet cats, while MERS-CoV emerged in humans through the intermediate host of camels. The precise way in which SARS-CoV-2 was transmitted from animals to humans is currently unknown. 

3. Is this virus comparable with SARS or with the seasonal flu?

The novel coronavirus detected in China in 2019, SARS-CoV-2, is closely related to the original SARS-CoV. Both viruses cause respiratory illnesses known as COVID-19 and SARS, respectively. Influenza, also known as the flu, is a respiratory illness with similar symptoms but caused by a different group of viruses, the influenza viruses.

SARS, the respiratory illness caused by the original SARS-CoV, 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.

COVID-19, caused by SARS-CoV-2, emerged in late 2019 and spread very quickly across the globe. As SARS-CoV-2 is a new virus, most people did not have immunity for it, so the entire human population was potentially susceptible to SARS-CoV-2 infection at the start of the pandemic. 

Within the first 20 months of the COVID-19 pandemic, 208 million cases were reported worldwide, 36 million alone in the EU/EEA. Due to the nature of the disease, where some infected individuals may not have symptoms and even those who do may not all be tested, it is assumed that there are many undiagnosed cases. The likelihood of death depends on age and is highest among older people. 

It is impossible to know when an influenza virus first infected humans, but convincing reports of influenza pandemics date back several hundred years. In a normal influenza year, about 1 in 1 000 people who develop seasonal flu die. The highest burden of disease of seasonal influenza is among children below the age of five years and in individuals older than 65 years of age. 

Both the virus causing COVID-19 and seasonal flu can spread between people who are in close contact with one another. Both are spread mainly by large and small particles containing virus that are expelled when people with the illness cough, sneeze or talk. The virus causing COVID-19 seems to spread more easily than influenza, and much more easily than SARS. The Delta variant is currently the most contagious SARS-CoV-2 virus isolated so far.

Vaccines against COVID-19 have only recently become available while influenza vaccines were developed as early as  the 1930s. No vaccine is available for SARS.

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4. How does the virus spread?

SARS-CoV-2 is mainly spread via respiratory droplets including aerosols from an infected person who sneezes, coughs, speaks, sings or breathes in close proximity to other people. Droplets including aerosols can be inhaled or deposited in the nose and mouth or on the eyes.

More rarely, infection may be due to contact with surfaces contaminated with droplets.

The virus can survive on different surfaces for a few hours (copper, cardboard) up to a number of days (plastic and stainless steel). However, the amount of viable virus declines over time and it is rarely present on surfaces in sufficient quantities to cause infection. Infection may occur when a person touches their nose, mouth or eyes with their hands either contaminated by fluids containing the virus or indirectly by having touched surfaces contaminated with the virus.  

We know that the virus can be transmitted by people up to two days before symptoms start, and when people who are infected show symptoms.

5. When is a person infectious?

SARS-CoV-2 can be detected in people one to three days before their symptoms start. However, detection of the virus does not necessarily mean that a person is infectious and able to transmit the virus to another person.

Evidence indicates that people become infectious around 48 hours before symptoms start, but are most infectious when having symptoms, even if symptoms are mild and non-specific. It appears that someone infected with the Delta variant may infect others earlier, within one two days of being exposed.

Available data indicate that adults with mild to moderate COVID-19 remain infectious no longer than 10 days after symptoms begin and this has not changed with the new variants of concern. Most adults with severe to critical illness or severe immune suppression likely remain infectious for up to 20 days after symptom onset.

For fully vaccinated individuals who become sick with COVID-19 (breakthrough infections), evidence shows that they can have comparable amounts of virus to non-vaccinated persons. However, they were less infectious overall as their ability to culture live virus was significantly less compared with non-vaccinated individuals.

6. How severe is COVID-19 infection?  

Most people infected with SARS-CoV-2 will experience mild to moderate respiratory illness and recover without requiring special treatment. COVID-19 can sometimes be a severe disease with respiratory insufficiency requiring intensive care and potentially leading to death.

Older people, and those with underlying medical problems like heart disease, diabetes, chronic respiratory disease and cancer are more likely to develop serious illness.

Available EU/EAA data show that up to 30% of people diagnosed with COVID-19 hospitalised are older. Hospitalisation is much less likely in younger people infected with COVID-19 if they do not have underlying medical conditions. Also, up to 20% of older people who are hospitalised may 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. Also, vaccinated individuals are less likely to have severe disease and to be hospitalised. The actual proportion of people who are hospitalised from the overall number of infected individuals is therefore lower than these figures suggest.

Page last updated 8 Sep 2021