Coronaviruses are a family of viruses that can cause respiratory illness in humans. They are called “corona” because of crown-like spikes on the surface of the virus. Severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS) and the common cold are examples of coronaviruses that cause illness in humans.

The new strain of coronavirus — SARS-CoV-2 — was first reported in Wuhan, China in December 2019. It has since spread to every country around the world.

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Coronaviruses are often found in bats, cats and camels. The viruses live in but don’t infect the animals. Sometimes these viruses then spread to different animal species. The viruses may change (mutate) as they transfer to other species. Eventually, the virus can jump from animal species and begin to infect humans. In the case of SARS-CoV-19, the first people infected are thought to have contracted the virus at a food market that sold meat, fish and live animals.

SARS-CoV-2, the virus that causes COVID-19, enters your body through your mouth, nose or eyes (directly from the airborne droplets or from the transfer of the virus from your hands to your face). It then travels to the back of your nasal passages and mucous membrane in the back of your throat. It attaches to cells there, begins to multiply and moves into lung tissue. From there, the virus can spread to other body tissues.

Coronavirus is likely spread:

If you have COVID-19 it can take several days to develop symptoms — but you’re contagious during this time. You are no longer contagious 10 days after your symptoms began.

The best way to avoid spreading COVID-19 to others is to:

Persons at greatest risk of contracting COVID-19 include those who:

The time between becoming infected and showing symptoms (incubation period) can range from two to 14 days. The average time before experiencing symptoms is five days. Symptoms can range in severity from very mild to severe. In about 80% of people, COVID-19 causes only mild symptoms, although this may change as variants emerge.

If you test positive for SARS-CoV-2 three months after your last positive test, it’s considered a reinfection. Before the omicron variant, reinfection with SARS-CoV-2 was rare but possible.

Omicron (B.1.1.529) was first reported in South Africa in November 2021 and quickly spread around the world. With many mutations, omicron was able to evade immune systems and we had more reinfections than ever before.

As the virus that causes COVID-19 continues to mutate, reinfection remains possible. Vaccination — including a booster dose — is the best protection against severe disease.