Reading numerous news articles about COVID-19, I got confused as to what is its main transmission route. In particular, I am confused as to whether it is

  • direct landing of respiratory droplets in mouths and noses,
  • contaminated surfaces,
  • aerosols (i.e., suspensions of the virus in the air rather than respiratory droplets quickly landing in mouths or noses or on surfaces), or
  • something else.

On the one hand, the website of the Centers for Disease Control and Prevention (CDC) says that contaminated surfaces are not thought to be the main transmission route:

It may be possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes, but this is not thought to be the main way the virus spreads. (Link)

The same website appears to suggest that the main transmission route is direct landing of respiratory droplets in mouths and noses:

The virus is thought to spread mainly from person-to-person.

  • Between people who are in close contact with one another (within about 6 feet).

  • Through respiratory droplets produced when an infected person coughs or sneezes.

These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.

On the other hand, the World Health Organization (WHO), like many other agencies, puts the main emphasis on washing hands. Here is the WHO's first and foremost piece of advice on how to prevent getting infected with the virus:

Regularly and thoroughly clean your hands with an alcohol-based hand rub or wash them with soap and water. Why? Washing your hands with soap and water or using alcohol-based hand rub kills viruses that may be on your hands. (Link)

Social distancing is mentioned on that webpage only as a second piece of advice, and, furthermore, the webpage implies that it is safe to approach coughing people as close as 1 meter away:

Maintain at least 1 metre (3 feet) distance between yourself and anyone who is coughing or sneezing.

Furthermore, I found an article saying that the virus wasn't detected in the air of hospital rooms with COVID-19 patients, but was detected on surfaces:

When researchers in Singapore tested the air in the rooms of three Covid-19 patients, they found no virus particles on cleaned surfaces or in the air even when they took samples on days the patients were symptomatic and presumably shedding virus into the air, they reported this month in the Journal of the American Medical Association. In the room of the third patient, who shed more virus, virus particles were present on ventilation fans and numerous surfaces — but all air samples were negative. (Link)

But the same article also says that Chinese researchers found COVID-19 aerosols near patients' toilets.

My question: Actually what is the main way COVID-19 spreads?


2 Answers 2


The confusion exists because there are conflicting pronouncements from various authoritative sources but also conflicting pronouncements from the same authority.

Covid-19 is a respiratory infection spread by droplets that can be aerosolized (nuclear droplets) in certain situations such as by flushing toilets or in certain medical procedures such as intubation. However, it reaches the air it contaminates surfaces and this allows for the infection to be caught through the eyes nose and mouth with the virus being transferred from the hand.

The data from Singapore and Taiwan show that handwashing and social distancing are successful in preventing disease transmission. However, if social distancing is not rigorously enforced then you will need to wear a mask. The head of the Chinese CDC, Dr George Gao, has recommended that everyone wear a mask which is advice that contradicts most countries health ministries. This is so that the infected are not shedding as many viral particles into the environment. His advice is based on the fact that there is a high degree of asymptomatic infection in the community and these people are spreading the virus by droplets just by talking and exhaling. The contrary advice is because they feel users are wearing masks to protect themselves, and, in the absence of training, they are almost certainly less effective at providing protection. But trained users have a similar degree of protection with both surgical masks and N95 masks.

So the main way of disease transmission is by respiratory droplet. But the fact that health workers, NYPD officers (currently over 500) and others are getting infected wearing masks points to surface contamination as the second main mode of infection, or, possibly lack of training in wearing the masks and/or poor hand washing, or, that aerosol transmission is indeed important.



  • 2
    From personal experience, wearing a mask prevents me from touching my face. So even if it offers only slight protection against inhalation of particles, it makes a major contribution to stopping me touching my nose and mouth. This, largely unconscious, habit is extremely hard to eradicate any other way. Commented Apr 1, 2020 at 13:33
  • I added an answer that's a July update and my own conclusions. I invite you to take a look and comment. Thanks!
    – chongman
    Commented Jul 31, 2020 at 22:49

The main way COVID19 spreads (according to experts) is either droplets (short distance, <6ft. short duration, <5 seconds from emission) OR aerosols (long distance, 20ft+, whole room. long duration, >60minutes)

Unfortunately, as of July 2020, we still don't know.

WHO has updated their modes of transmission: https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions

July 9.

They say there isn't hard evidence of for H1: aerosol>droplet, so they are sticking to their null hypothesis H0: droplet > aerosol. However, the detractors say there isn't hard evidence for H0 either.

After talking to several doctors and chemists and reading about 5-10 articles, my conclusion (i.e. educated guess) is that it's about a tie between droplets and aerosols.

The key details can be found in the OPTIONAL section of this 10 minute science communication piece (http://tinyurl.com/covid3particles).

It's endogenous -- the main mode of transmission depends on what protective practices are in place.

  • If you 100% protect against droplets, then aerosols will probably be the main mode.
  • If you use no protection, then droplets are probably the main mode.
  • If you are never in someone else's room (except after airing it out), then fomites (surfaces) might be the main route. But only because you eliminated everything else.

You can also look at the CHAIN model. (tinyurl.com/CHAINmodel) especially the end of the article.

Surfaces and soap are, unfortunately, not foolproof/complete protection.

There are many people who wash their hand religiously. They still can get sick. So, we know that perfect hand washing won't stop it.

PS: Agree with @Graham's answer

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