SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus that causes COVID-19, a respiratory illness that led to a major worldwide health crisis called the COVID-19 pandemic. This virus was first found in the city of Wuhan in China in late 2019. The World Health Organization declared it a serious global health concern from January 30, 2020, to May 5, 2023.

SARS-CoV-2 belongs to a group of viruses called coronaviruses, just like the virus that caused an earlier outbreak called SARS-CoV-1 in 2002–2004. Scientists believe this virus came from animals, most likely bats, and may have passed through another animal before affecting people. The virus spreads mainly through close contact and tiny particles released when an infected person talks, breathes, coughs, or sneezes. It can enter human cells by attaching to a specific protein called angiotensin-converting enzyme 2 (ACE2).

Understanding SARS-CoV-2 helps us know how to stay safe and prevent the spread of COVID-19.

Terminology

When the virus was first found in Wuhan, China, people called it many things, like "the coronavirus." In January 2020, the World Health Organization suggested using "2019 novel coronavirus" as a temporary name.

Later, scientists officially named the virus "severe acute respiratory syndrome coronavirus 2" (SARS‑CoV‑2). The WHO sometimes calls it "the COVID-19 virus" to keep it clear from the sickness it causes. The WHO says calling it the "Wuhan virus" can be unfair.

Infection and transmission

Main article: Transmission of COVID-19

People can spread the virus that causes COVID-19 from one person to another. This was proven in January 2020 during the COVID-19 pandemic. The virus spreads mainly when someone coughs or sneezes, sending out tiny drops of liquid that can land on another person within about 1.8 metres, or 6 feet. Talking can also spread the virus far inside rooms with little air flow. Some studies think the virus can float in the air and be spread that way, too. Touching surfaces that have the virus on them can also make people sick. Research shows the virus can live on plastic and stainless steel for up to three days.

The virus can be spread even before someone feels sick. Some animals, like cats, can also get infected with the virus.

There is still much we do not know about getting the virus again after recovering. The first known case of someone getting the virus again happened to a man in Hong Kong. He got the virus, recovered, and then tested positive again later. Tests showed he had gotten a different version of the virus the second time. This shows that being infected once may not protect someone from getting the virus again.

Reservoir and origin

Further information: Origin of SARS-CoV-2

We do not know where the virus that causes COVID-19, called SARS-CoV-2, naturally lives. Before this virus, there were two other coronavirus diseases that came from animals: one caused by SARS-CoV-1 and another by MERS-CoV.

The first people known to get sick with SARS-CoV-2 were in Wuhan, China. We still do not fully understand where the virus came from or how it first spread to people. Many early patients worked at a seafood market in Wuhan, leading some to think the virus may have started there. But other research suggests people may have brought the virus to the market, where it then spread quickly. A report in 2021 suggested that the virus likely jumped to people from an animal, with bats being the next most likely source. It is also possible the virus came through our food supply, though this seems less likely.

Coronaviruses, like SARS-CoV-2, usually change quickly as they spread. However, SARS-CoV-2 changes more slowly than some other viruses because of how it copies itself. Scientists have found many similar viruses in bats, but none are exactly the same as SARS-CoV-2. Bats are thought to be the most likely natural home for this virus, but we do not know for sure how it first reached people.

Phylogenetics and taxonomy

SARS-CoV-2 is a type of virus called a coronavirus. It can infect humans and animals. Most coronaviruses cause mild illnesses like the common cold, but some can cause more serious diseases. SARS-CoV-2 is the seventh known coronavirus to infect people.

This virus has a long genetic code. Scientists study it to understand how it changes and spreads. By looking at the genetic code, researchers can trace how the virus evolved and moved around the world. In early 2020, scientists began sharing the genetic codes of many versions of the virus. This helped them build family trees showing how the virus changed over time.

Main article: Variants of SARS-CoV-2

There are many different versions, or variants, of SARS-CoV-2. Some variants have changed in ways that make them spread more easily. The World Health Organization has identified several important variants that need special attention. These include variants first found in the United Kingdom, South Africa, Brazil, India, and Botswana. Each of these variants has unique changes in their genetic code.

Virology

SARS-CoV-2, the virus that causes COVID-19, is very small, measuring between 60 and 140 nanometres across. It has four main parts: the spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins. The spike protein helps the virus attach to and enter human cells.

The virus’s genetic code, or genome, is a single piece of RNA about 30,000 bases long. Scientists have studied many of these genomes to learn more about the virus. The genome helps the virus copy itself inside cells and avoid some of the body’s natural defenses.

Virus infections begin when the virus attaches to a specific protein on human cells called ACE2. Once attached, the virus uses tools to break into the cell, release its RNA, and make the cell produce more copies of itself. These new virus particles then go on to infect other cells. The virus also makes proteins that help it spread and avoid the body’s immune system.

Treatment and drug development

Main article: Treatment and management of COVID-19

There are very few medicines that work well against the virus that causes COVID-19. One medicine called Masitinib was tested in animals and showed it could lower the amount of virus, but it is not approved for people with COVID-19. In December 2021, the United States allowed a medicine called Nirmatrelvir/ritonavir to be used in special cases to help treat the virus. Soon after, the European Union, the United Kingdom, and Canada also approved it.

The COVID Moonshot is a global effort that began in March 2020. It aims to create an easy-to-take medicine to treat the virus, and it is shared openly so that everyone can use it.

Epidemiology

Main article: COVID-19 pandemic

Tests done later in Wuhan, China, showed that many people may have had the virus without knowing it in late 2019.

Studies from November 2020 looked at how easily the virus spreads. They found that each person with the virus could infect a few other people if no one was protected and no precautions were taken. In crowded places like cruise ships, the virus could spread even more. Different countries and cultures saw different spread rates because of how people lived. Some places had lower spread rates, while others had higher rates. Later versions of the virus spread more easily. One version, called Omicron, spread very quickly.

In the early weeks of the pandemic, there were many confirmed cases in China. Most early deaths from the illness happened in the area around Wuhan.