• COVID-19 is an infectious disease caused by the novel coronavirus SARS-CoV-2.
• SARS-CoV-2 originates from the same family of viruses with the Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV), but it is not the same virus.
• This new virus, named SARS-CoV-2, has not been previously identified in humans before the ongoing outbreak that was first identified in Wuhan, China in December 2019.
• COVID-19 causes illness ranging from mild respiratory symptoms to severe complications and death.

• While the SARS-CoV-2 virus originated in animals and the initial human cases were "zoonotic", the virus has been transmiting from person to person since December 2019.
• There is increasing information on how SARS-CoV-2 spreads from one person to another. Most transmission seems to occur after prolonged close contact with an infected case. The possible transmission modes of the virus at present are thought to be similar to other respiratory viruses:
• Droplets
• Direct contact
• Indirect contact via contaminated surfaces
• Aerosols (fine particles) mainly at close range
• Possibly through fecal-oral route because coronaviruses can also infect the gastrointestinal tract
• At present, we are also uncertain if there is one transmission mode that is more important than the others, and this is an important scientific question which we are trying to answer.
• Usually, infected persons are most contagious around the time that their symptoms appear. There is growing evidence that asymptomatic or pre-symptomatic transmissions are important for SARS-CoV-2, where infected persons can be infectious even without showing any symptoms or before their symptoms appear.

• As with some other respiratory viruses, COVID-19 has a broad clinical spectrum. Some infected persons show no symptoms, others could range from mild respiratory illness to severe complications and life-threatening illness. A small fraction of illnesses have been fatal. Symptomatic cases commonly have fever, malaise and respiratory symptoms such as dry cough and shortness of breath, and some have other symptoms such as aches and pains, nasal congestion, headache, conjunctivitis, sore throat, diarrhoea, or loss of taste or smell. Some identified cases have pneumonia.
• Symptomatic cases usually show clinical signs and illness 1–14 days after they have been infected, most commonly around 5 days.
• At present, older adults and adults with underlying health conditions appear to be at the highest risk of severe disease.

Several vaccines for COVID-19 prevention have recently been rolled-out for use under different conditions (e.g. early use, emergency use, limited use) in a number of countries. Dozens of other candidate vaccines are in different stages of development, from pre-clinical investigation to large-scale trial. The health system in most jurisdictions adopt a priority-based allocation framework for the COVID-19 vaccine, enabling populations with highest risks to be vaccinated first, such as health care workers, elderly and those with pre-existing diseases.

For populations who have not yet received the vaccine, preventive measures are mostly non-pharmaceutical:

• Personal protective measures
  • Maintain good hand hygiene
  • Practice good respiratory etiquette
  • Wear a surgical mask
  • Avoid touching eyes, nose and mouth


• Environmental hygiene
  • Disinfect frequently touched objects and surfaces
  • Inspect drainage pipes regularly and make sure the drain outlets contain water by adding half a litre of water into each drainage trap (U-trap) about once a week


• Social distancing measures
  • Isolation of infected persons at home or in hospitals
  • Quarantine of potentially infected persons (e.g. those who have been in prolonged close contact with known cases) either at home or in special quarantine facilities
  • Refrain from visiting crowded places
  • Maintain (at least 3 feet) distance from other persons, especially those who are showing respiratory illness symptoms
  • Workplaces can consider measures such as working from home or working in staggered shifts

• The U.S. FDA have recently approved the antiviral drug remdesivir for the treatment of specific groups of hospitalized COVID-19 patients. There is not yet other specific antiviral treatment recommended for COVID-19 patients and current treatment is mainly supportive, that is to relieve clinical symptoms.
• There are ongoing investigations for specific treatments for COVID-19 other than remdesivir, including other antivirals administered singly or in combination, and convalescent plasma.

• Researchers are trying to gain better understanding on the transmission dynamics and severity of COVID-19 from documentations of outbreaks and chains of transmission.
• This information would affect how control and mitigation measures should be implemented, for example, the incubation period and viral shedding of infected persons would provide insights on the duration of quarantine and isolation respectively.
• The latest research conducted by HKU SPH on COVID-19 is available in the "Scientific research" section.