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On 31 December 2019, the World Health Organization (WHO) was informed of a cluster of cases of pneumonia of unknown cause detected in Wuhan City, Hubei Province, China.
On 9 January 2020, it was announced that a novel coronavirus had been identified in samples obtained from these cases and that initial analysis of virus genetic sequences suggested that this was the cause of the outbreak. This virus is referred to as SARS-CoV-2, and the associated disease as COVID-19.
The WHO coronavirus dashboard has international information on cases, deaths and vaccine doses administered. WHO also publishes aweekly international epidemiological and operational updates.
The number of confirmed cases in the UK is published daily on a visual dashboard.
Coronaviruses are a large family of viruses with some causing less severe disease, such as the common cold, and others causing more severe disease, such as Middle East respiratory syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS) coronaviruses. They are a different family of viruses to the Influenza viruses that cause the seasonal flu.
Nomenclature and characterisation
On 11 February 2020, WHO named the syndrome caused by this novel coronavirus COVID-19 (Coronavirus Disease 2019) using its best practice guidance. The Coronavirus Study Group (CSG) of the International Committee on Taxonomy of Viruses named the causative agent as ‘severe acute respiratory syndrome coronavirus 2’ (SARS-CoV-2). The virus belongs to a group of genetically related coronaviruses that includes SARS-CoV and viruses isolated from bat populations. MERS-CoV also belongs to this group but is less closely related.
The 2019 emergent SARS-CoV-2 strain, usually referred to as the ‘original’ or ‘wild’ strain has changed or mutated over time. These mutations have given rise to new variants. Variants of the SARS-CoV-2 virus are being monitored by the UK Health Security Agency (UKHSA) and other agencies across the world, including WHO.
Most changes in the virus have little effect. Where changes have the potential to increase how fast or easily the virus spreads, escape immunity, cause more severe disease, or to reduce the effectiveness of treatment or control measures, the variant is designated a Variant Under Investigation (VUI). Where there is clear evidence of an effect on these factors, the variant is designated a Variant of Concern (VOC). On 31 May 2021, the WHO recommended a naming system for VUIs and VOCs of the SARS-CoV-2 virus that uses the Greek alphabet. UKHSA incorporates this recommended naming system in its surveillance of SARS-CoV-2 variants, and releases weekly information on VUIs and VOCs.
The source of the original outbreak is yet to be determined. A zoonotic (animal) source has not been identified, but investigations are ongoing.
SARS-CoV-2 is primarily transmitted between people through respiratory particles (droplet and aerosol) and indirect contact through fomite transmission (contact with contaminated surfaces). When someone with COVID-19 breathes, speaks, coughs or sneezes, they release droplet or aerosol particles containing SARS-CoV-2. Aerosol particles can also be released when certain procedures or support treatments are performed in health and care settings. A person can be infected when these particles are inhaled, or come into contact with the eyes, nose or mouth.
Transmission risk is highest where people are in close proximity (particularly within 2 metres) and/or in poorly ventilated indoor spaces, particularly if individuals are in the same room together for an extended period of time.
Transmission of SARS-CoV-2 is occurring across the world. Therefore precautions are required to prevent spread of the virus (see the UK Government’s suite of guidance for staying safe during the coronavirus (COVID-19) pandemic.
It is possible for humans to transmit SARS-CoV-2 to other mammals including dogs, cats, and farmed mink. However, there is limited evidence on whether or not infected mammals pose a significant risk of infection to humans.
COVID-19 presents with a range of symptoms of varying severity. It is estimated that 1 in 3 people have COVID-19 without displaying any symptoms.
The main symptoms include fever, a new and continuous cough, anosmia (loss of smell) and ageusia (loss of taste). Examples of other symptoms include, shortness of breath, fatigue, loss of appetite, myalgia (muscle ache), sore throat, headache, nasal congestion (stuffy nose), runny nose, diarrhoea, nausea and vomiting.
Of those who develop symptoms, current data indicate that 40% have mild symptoms without hypoxia (low blood oxygen levels) or pneumonia, 40% have moderate symptoms and non-severe pneumonia, 15% have significant disease including severe pneumonia, and 5% experience critical disease with life-threatening complications. Refer to guidance on the investigation and initial clinical management of possible cases for further information.
Critical disease includes acute respiratory distress syndrome (ARDS), sepsis, septic shock, cardiac disease, thromboembolic events, such as pulmonary embolism and multi-organ failure.
Atypical symptoms, such as delirium and reduced mobility, can present in older and immunocompromised people, often in the absence of a fever.
Infants and children generally appear to experience milder symptoms than adults and require admission to hospital less frequently. The risk of death in children is extremely low and appears linked to severe comorbidities. There are a number of ongoing surveillance programmes to monitor the course, progression and outcomes of COVID-19 in children. A very rare multisystem inflammatory response (paediatric multisystem inflammatory syndrome (PIMS)) associated with COVID-19 in children and adolescents has been noted.
Risk of severe disease and death is higher in people who are older, male, from deprived areas or from certain non-white ethnic backgrounds. Certain underlying health conditions, as well as obesity, also increase risk of severe disease and death in adults.
COVID-19 vaccination significantly reduces the risk of infection, hospitalisation and death. However, fully vaccinated individuals can still become infected with SARS-CoV-2.
There is growing evidence to suggest that individuals who have suffered from both mild or severe COVID-19 can experience prolonged symptoms or develop long-term effects. Refer to the long-term health effects guidance for further information.