COVID-19: Main modes of transmission

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How COVID-19 spreads

SARS-CoV-2, the virus that causes COVID-19, spreads from an infected person to others through respiratory droplets and aerosols when an infected person breathes, coughs, sneezes, sings, shouts, or talks. The droplets vary in size, from large droplets that fall to the ground rapidly (within seconds or minutes) near the infected person, to smaller droplets, sometimes called aerosols, which linger in the air, especially in indoor spaces.

The relative infectiousness of droplets of different sizes is not clear. Infectious droplets or aerosols may come into direct contact with the mucous membranes of another person's nose, mouth or eyes, or they may be inhaled into their nose, mouth, airways and lungs. The virus may also spread when a person touches another person (i.e., a handshake) or a surface or an object (also referred to as a fomite) that has the virus on it, and then touches their mouth, nose or eyes with unwashed hands.

Settings with higher risk of transmission

Outbreak investigations and scientific studies are revealing more about COVID-19 and this new knowledge is being applied to reduce its spread. We know that the virus is most frequently transmitted when people are in close contact with others who are infected with the virus (either with or without symptoms). We also know that most transmission occurs indoors.

Reports of outbreaks in settings with poor ventilation suggest that infectious aerosols were suspended in the air and that people inhaled the virus at distances beyond 2 metres. Such settings have included choir practice, fitness classes, and restaurants, as well as other settings. Transmission can be facilitated by certain environmental conditions, such as re-circulated air. Activities that increase generation of respiratory droplets and aerosols may increase risk in these settings (such as singing, shouting, or exercising).

It is still unclear how easily the virus spreads through contact with surfaces or objects.

Follow public health measures

While we do not yet fully understand all modes of transmission and their relative importance, it is likely that multiple modes of transmission occur.

The public health measures that we have been practising continue to be effective in preventing the spread of the virus that causes COVID-19. To protect yourself and others, use multiple personal preventive practices at once in a layered approach. With the increased circulation of some variants of concern, it is even more important that you strictly follow recommended personal preventive practices.

Ventilation

Maximize ventilation by ensuring that heating, ventilation and air conditioning (HVAC) systems are in good working order. Drawing as much fresh air as possible from outside will decrease the concentration of aerosols that may be suspended in the air, and reduce the chances of SARS-CoV-2 spread if those aerosols happen to contain the virus. If the weather permits, open a window. Reduce the noise level in public spaces, for example turn off or reduce the music volume, so people can speak quietly.

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