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In December 2019, several cases of pneumonia of unknown aetiology were detected in Wuhan, China.
These were caused by a novel beta coronavirus, SARS-CoV-2.
The disease, termed coronavirus disease 2019 (COVID-19), rapidly spread around the world, ranking among the deadliest epidemics in history.
Coronaviruses comprise a large family of enveloped positive stranded RNA viruses.
They have a crown-like appearance under the electron microscope, hence are named after the Latin word ‘corona’, meaning crown.
Compared with other RNA viruses, coronaviruses are characterised by low mutation rate, although this appears to have increased in more recent variants.
The clinical symptoms can be mild or severe. The mild ones involve headaches, low-grade fever, mild fatigue and at least with early variants, a loss or change to the sense of smell or taste.
More severe symptoms include a continuous cough, shortness of breath and difficulty breathing, nausea, vomiting and diarrhoea.
At worst, this disease can result in loss of consciousness and death.
SARS-CoV-2 is usually spread through droplets produced by an infected person's cough or sneeze as well as aerosols suspended in the air for a long time in an enclosed space.
Contact with objects infected by the virus is now thought a less likely source of transmission.
People over the age of 60 years those who have health conditions like lung or heart disease, diabetes or conditions that affect their immune system as well essential workers are at the highest risk of contracting COVID-19.
It is usually diagnosed by either the reverse transcription polymerase chain reaction (RT-PCR) which detect viral RNA, or by antigen tests using lateral flow devices, which detect the viral spike protein.
Variants are most readily identified by direct RNA sequencing of the viral genome and past infections can be detected by antibody testing.
As of May 7, 2021, the World Health Organization has approved several vaccines for emergency use worldwide.
Vaccination is the most effective way to reduce the risk of developing severe COVID-19 and it also reduces the risk of spreading it to other people.
Importantly, vaccination coverage rate is also inversely correlated to the mutation frequency of the SARS-CoV-2.
Other public health measures include meeting people outside if possible, ventilating indoor spaces by opening doors and windows, limiting the number of people meeting to avoid crowded places, wearing a mask indoors in public places, washing hands with soap and using alcohol-based hand sanitiser regularly throughout the day.