The coronavirus SARS-CoV-2 is the virus that can cause the disease known as COVID-19. The virus is spread through human-to-human transmission. Coughing and sneezing spreads small droplets. Someone else can breathe them in and become infected. The droplets can also be transmitted through hand contact, for example if someone touches their nose or face and then shakes hands.

About viruses

Viruses are micro-organisms. They are so small that they cannot be seen with an ordinary microscope. A virus cannot do anything on its own. Essentially, a virus particle is no more than a piece of genetic material – deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) – enclosed inside a layer of proteins. There are many different types of viruses.

How a virus works

Viruses cannot exist and thrive without a host. A virus needs host cells from a living creature, for example a human. Inside the host, the virus penetrates the healthy cells and then starts replicating itself. The cell very quickly produces a huge number of virus particles known as virions. The new virions that are released go on to infect new cells. That is how a carrier of the virus becomes ill. 

Once your immune system detects the presence of these virus cells, it responds in various ways – for example by creating antibodies, which try to destroy the virus. Those antibodies remain in the body for some time, even after you are completely recovered. 

The coronavirus SARS-CoV-2

There are many different types of viruses, including a family known as the ‘coronaviruses’. Examples include the coronavirus that causes Middle East Respiratory Syndrome (MERS-CoV) and the coronavirus that causes Severe Acute Respiratory Syndrome (SARS-CoV1) and was the virus behind the SARS epidemic in 2003.  The coronavirus that causes COVID-19 is officially called SARS-CoV-2.

A coronavirus has a striking and specific shape. If you look at the virus under an electron microscope, you will see that it is covered in club-shaped spikes. The overall form resembles a crown. The Latin word for crown is ‘corona’. The name of the virus comes from its shape.

Visual COVID-19: name coronavirus and why a virus needs humans

Download the poster COVID-19: from infection to symptoms

A virus changes constantly

Viruses are constantly changing. The coronavirus SARS-CoV-2 originated as a human virus in one single location in China in December 2019. Since then, the virus has been travelling all over the world, and its genetic code has changed slightly along the way; this is referred to as a mutation. There are thousands of variants of the virus by now.  Different variants of the virus are circulating in the Netherlands as well. RIVM monitors those variants closely in the context of pathogen surveillance

Read more about the different variants of the virus

RIVM research on variants of the virus

Random samples are taken in the Netherlands on an ongoing basis to research the virus and determine whether it is changing. The Alpha variant, Beta variant and Delta variant and the Gamma variants P1 and P2 of the virus were detected in the Netherlands in the context of ‘pathogen surveillance’. In this joint research programme, which RIVM, Erasmus MC and 21 laboratories in the Netherlands are working together. The laboratories regularly send a random sampling of the test samples to RIVM or Erasmus MC, where they are examined. This makes it possible to map which virus variants are occurring in different locations in the Netherlands. This research is called sequence analysis. 

Poster on coronavirus SARS-CoV-2 (COVID-19)

Visual on spread and infection COVID-19

Download the poster COVID-19: from infection to symptoms

How weather affects the virus

We know that many respiratory viruses spread less easily when the weather is warmer and sunnier. This ‘seasonal effect’ also seems to apply to SARS-CoV-2.

There are multiple factors that could play a role in this seasonal variation. Among other things, weather has an effect on our behaviour and on our immune systems.  However, the virus does not vanish completely in summer. SARS-CoV-2 also spreads in countries with a warm and sunny climate.