Through what primary routes does the virus that causes COVID-19 spread from person to person?
Current evidence suggests that COVID-19 spreads primarily between people through direct, indirect (through contaminated objects or surfaces), or close contact with infected individuals via mouth and nose secretions. These secretions include saliva, respiratory secretions, or droplets. They are released from the mouth or nose of an infected person when they cough, sneeze, speak, or sing. People in close contact (within about 1 metre) with an infected person can contract COVID-19 when these infectious droplets enter their mouth, nose, or eyes.
To avoid exposure to droplets, it is essential to maintain a distance of at least 1 metre from others, wash hands frequently, and cover your mouth and nose with a tissue or your bent elbow when coughing or sneezing. When physical distancing (maintaining at least 1 metre apart) is not feasible, wearing a fabric face mask helps protect those around you. Frequent hand hygiene is crucial to prevent infection.
What are other potential routes of COVID-19 transmission?
Individuals with the virus in their nose and throat can inadvertently contaminate objects and surfaces (known as fomites) with infectious droplets when they cough, sneeze, or touch surfaces such as tables, doorknobs, and handrails. Other individuals can become infected by touching these contaminated objects or surfaces and then touching their eyes, nose, or mouth before washing their hands.
Therefore, it is vital to clean hands thoroughly and frequently with soap and water or an alcohol-based hand rub, and to regularly clean and disinfect surfaces.
What is known about airborne transmission?
Certain medical procedures can generate very small droplets (known as droplet nuclei or aerosols) that remain suspended in the air for longer periods. When these procedures are performed on COVID-19 patients in healthcare settings, the resulting aerosols may contain the virus. Other individuals can inhale these infectious aerosols if they do not wear appropriate personal protective equipment (PPE). Consequently, all healthcare workers must implement appropriate airborne precautions when performing medical procedures, including the use of suitable PPE. Visitors are not permitted in areas where such medical procedures are conducted.
Reports of COVID-19 outbreaks in indoor settings such as restaurants, nightclubs, places of worship, or areas where people shout, talk, or sing suggest the possibility of aerosol transmission, particularly in poorly ventilated indoor spaces where infected individuals spend prolonged periods with others. Urgent research is needed to investigate such events and assess COVID-19 transmission in these environments.
When can an infected person transmit the virus?
Based on current knowledge, COVID-19 is primarily transmitted from symptomatic individuals, but transmission can also occur just before symptoms develop during close, prolonged contact with others. Asymptomatic individuals can also transmit the virus to others; however, the extent of this transmission remains unclear and requires further investigation.
Limiting contact with COVID-19 patients, practicing thorough and frequent hand hygiene, and wearing masks when a physical distance of at least 1 metre cannot be maintained help interrupt transmission.
Can asymptomatic individuals transmit the virus?
Yes. Infected individuals can transmit the virus both when they have symptoms and when they do not. Therefore, identifying infected cases through testing, isolation, and medical care is essential, depending on disease severity. Even individuals diagnosed with COVID-19 who remain asymptomatic must be isolated to limit contact with others. These measures aim to curb the spread of the disease.
Always maintain a physical distance of at least 1 metre from those around you, cover your mouth and nose with your inner elbow or a tissue when coughing or sneezing, wash your hands frequently, and stay home if you feel unwell or are instructed to do so. In areas with widespread community transmission, the public should wear fabric masks when physical distancing and other control measures cannot be implemented.
Further information on the use of masks is available here.
What is the difference between asymptomatic and pre-symptomatic individuals? Does this mean they do not have symptoms?
Yes, both terms refer to individuals without symptoms. The distinction is that asymptomatic refers to people who are infected but develop no symptoms throughout the course of their infection, whereas pre-symptomatic refers to those who are infected but have not yet developed symptoms, which appear later.
This distinction is critical for public health strategies aimed at controlling transmission. For instance, testing data indicate that individuals are most infectious around the time they develop symptoms. Consequently, in WHO guidance on case investigation and contact tracing, a 'contact' is defined as someone who has had exposure to an infected person from 2 days before that person's symptom onset.
Is further information needed to better understand the transmission mechanisms of COVID-19?
Yes. COVID-19 is a novel disease. While information is continuously emerging and updated daily, many questions regarding its transmission dynamics remain. Numerous research groups and networks worldwide are working to find answers.
WHO and its partners are collaborating to better understand:
- transmission routes, including droplet transmission of varying sizes, direct contact, fomites, and the role of airborne transmission in the absence of aerosol-generating procedures;
- the infectious dose required to transmit the disease;
- patient characteristics and settings that drive superspreading events, as observed in certain indoor environments;
- the proportion of infected individuals who remain asymptomatic throughout their infection;
- the proportion of truly asymptomatic individuals who transmit the virus to others;
- specific risk factors associated with asymptomatic and pre-symptomatic transmission; and
- the overall proportion of infections originating from asymptomatic and pre-symptomatic individuals.
What does WHO recommend to prevent or control COVID-19?
WHO recommends a comprehensive package of interventions to prevent person-to-person transmission of COVID-19:
- Limit close contact between infected individuals and others. Maintain a physical distance of at least 1 metre from others. In areas where COVID-19 is circulating and this distance cannot be maintained, wear a mask.
- Promptly identify infected individuals for isolation and care, and ensure that their contacts are quarantined in appropriate facilities.
- Practice frequent hand hygiene and always cover your mouth and nose with a tissue or your inner elbow when coughing or sneezing.
- Avoid crowded places, close-contact settings, and confined, poorly ventilated indoor spaces.
- Ensure adequate indoor ventilation in homes and workplaces.
- Stay home if you feel unwell, and contact a healthcare provider or facility as soon as possible to determine if medical attention is needed.
- In countries and territories with community transmission of COVID-19, healthcare workers should continuously wear medical masks during all routine activities in clinical areas of healthcare facilities.
- Healthcare workers must also use additional personal protective equipment and precautions when caring for COVID-19 patients. Further details for healthcare workers are available here and here.
- Implement appropriate occupational health and safety measures in the workplace, as detailed here.
How can I protect myself against COVID-19?
Find further information on protective measures for yourself here.
What is the purpose of scientific briefs on disease transmission?
WHO regularly publishes scientific briefs to provide in-depth explanations of specialized topics for scientific audiences. The scientific brief on COVID-19 transmission summarizes current knowledge on how the virus spreads between people, who transmits it, when transmission occurs, and the implications of preventive measures. It also highlights key research areas that will help inform future recommendations and guidelines.
This information is crucial for understanding preventive measures and limiting the spread of the virus among humans.
WHO scientific briefs are living documents, meaning they are updated as new research becomes available. COVID-19 is a novel disease, and our understanding of it evolves daily.
How does WHO synthesize information?
WHO continuously reviews published research, including studies in preprint servers (manuscripts that have not yet been peer-reviewed). WHO also identifies critical questions that need to be answered to improve responses to the COVID-19 outbreak and guides research priorities on these issues. WHO convenes regular virtual meetings with global networks of experts across scientific disciplines to evaluate all available research, assess current evidence, and incorporate best practices and frontline experiences into guidance and recommendations.
Source: https://www.who.int/vietnam/vi/news/detail/14-07-2020-q-a-how-is-covid-19-transmitted