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Coronaviruses are a group of related viruses that cause disease. In humans, coronaviruses cause respiratory infections that can be mild or serious.
The spherical shells of coronaviruses are covered in spikes that allow the virus to attach to our cells. These spikes, which are made up of proteins, give the appearance of a crown – or corona – hence the name coronavirus. Understanding the structure of the protein spike is important for designing drugs and vaccines to block their entry to our cells.
There are many types of coronaviruses. The virus that causes the common cold is a coronavirus. Coronaviruses are all single strand RNA viruses as opposed to the double strand genetic structure of DNA. Despite sharing similar symptoms, influenza is not caused by a coronavirus, but by a different type of virus altogether.
Seven coronaviruses that can infect humans have been identified. In addition to the common cold coronavirus, others are SARS (Severe Acute Respiratory Syndrome) which caused two epidemics in 2003 and 2005, and MERS (Middle Eastern Respiratory Syndrome). The coronavirus that causes Covid-19 (coronavirus disease 2019) is related to SARS. It’s official name is SARS-CoV-2, but the world knows it as Covid-19.
Covid-19 is very infectious because it does not kill many of its hosts. Since the virus first emerged, a number of changes to its genetic code have occurred. These changes can cause the virus to act in different ways. Significant alterations are known as variants. Scientists give each variant a Greek letter of the alphabet to denote each significant change, and an ‘R’ value to indicate how many people one person is likely to infect. Omicron is the latest variant to emerge and is the most infectious to date. Its R value is believed to be around three to four, meaning one person can infect up to four other people.
People who have Covid-19 may not show any or many symptoms. Because of this they can unknowingly pass the virus on to others at home, at school and at work. People vaccinated against Covid-19 can also pass the virus on, but are protected from developing more severe illness.
Covid-19 has the transmissibility of a common cold virus, but is more closely aligned in severity to SARS and MERS, a combination of genetic traits that led to the world to go into rotating lockdowns as variants emerged.