Changing views of how COVID spreads

Throughout much of 2020, the World Health Organization (WHO) held tight to the idea that SARS-CoV-2, the virus that causes COVID-19, spreads through relatively large ‘respiratory’ droplets that are expelled by infected people while coughing, sneezing or speaking. These droplets contaminate nearby surfaces or get breathed in, so the WHO stressed the importance of washing hands and disinfecting surfaces.

It took many months for the agency to acknowledge that the virus could travel on tiny particles called aerosols that can spread widely and linger in the air. And nearly two years passed before the WHO clearly stated that the virus is airborne.

Scroll horizontally to move through the timeline of WHO statementsabout transmission of COVID-19:

  • 23 February 2020

    The WHO does not mention transmission by means of aerosols, or that the virus can spread across distances of more than one metre or remain in the air.

    “The disease can spread from person to person through small droplets from the nose or mouth which are spread when a person with COVID-19 coughs or exhales. These droplets land on objects and surfaces around the person. Other people then catch COVID-19 by touching these objects or surfaces, then touching their eyes, nose or mouth. People can also catch COVID-19 if they breathe in droplets from a person with COVID-19 who coughs out or exhales droplets. This is why it is important to stay more than 1 metre (3 feet) away from a person who is sick.”

  • 28 March 2020

    The agency explicitly states that the virus is not airborne, despite reports at the time suggesting that it could be.

    “FACT: #COVID19 is NOT airborne …”

    “The virus that causes COVID-19 is mainly transmitted through droplets generated when an infected person coughs, sneezes or speaks.”

    “These droplets are too heavy to hang in the air. They quickly fall to the ground.”

  • 9 July 2020

    In a detailed ‘Scientific Brief’, the WHO continues to stress that transmission is through droplets that fall onto surfaces and are spread by surface contamination or by close contact. But, for the first time, it acknowledges that transmission by aerosols outside of medical settings might be possible, contradicting its previous statements.

    “Outside of medical facilities, some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, for example, during choir practice, in restaurants or in fitness classes. In these events, short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons cannot be ruled out.”

  • 20 October 2020

    The WHO states that aerosol transmission happens outside of medical settings.

    “Current evidence suggests that the main way the virus spreads is by respiratory droplets among people who are in close contact with each other. Aerosol transmission can occur in specific settings, particularly in indoor, crowded and inadequately ventilated spaces, where infected person(s) spend long periods of time with others, such as restaurants, choir practices, fitness classes, nightclubs, offices and/or places of worship. More studies are under way to better understand the conditions in which aerosol transmission is occurring outside of medical facilities where specific medical procedures, called aerosol generating procedures, are conducted.”

  • 30 April 2021

    The WHO for the first time mentions that aerosols can stay suspended in the air or travel long distances.

    “Current evidence suggests that the virus spreads mainly between people who are in close contact with each other, typically within 1 metre (short-range). A person can be infected when aerosols or droplets containing the virus are inhaled or come directly into contact with the eyes, nose, or mouth.

    The virus can also spread in poorly ventilated and/or crowded indoor settings, where people tend to spend longer periods of time. This is because aerosols remain suspended in the air or travel farther than 1 metre (long-range).”

  • 23 December 2021

    Nearly two years into the pandemic, the WHO uses the term ‘airborne’ for the first time.

    “Current evidence suggests that the virus spreads mainly between people who are in close contact with each other, for example at a conversational distance …

    The virus can also spread in poorly ventilated and/or crowded indoor settings, where people tend to spend longer periods of time. This is because aerosols can remain suspended in the air or travel farther than conversational distance (this is often called long-range aerosol or long-range airborne transmission).”