COVID-19 Manual Section 2: Transmission of COVID-19


COVID-19 appeared as a new and unknown disease in Wuhan, China in late 2019.

Initial research identified that it was being spread by contact with infected people who came into direct contact with other people, or touched surfaces which others then touched, and by so doing so picked up the virus.

Public Health England (PHE) published guidance based on surface transmission: ‘Transmission of SARS-CoV-2 and Mitigating Measures’, now available on the UK Government website.

PHE have updated their guidance as more information on COVID-19 has come available, and are now providing guidance on airborne and surface transmission. Their website is updated regularly and remains a source of the current UK Government advice including access to various sector guidance.

Since COVID-19 arrived, there has been a significant change in the basic assumptions (as described above), and an understanding that COVID-19 is an airborne virus which can infect people through airborne routes and also through surface routes as, and when, airborne virus settles onto surfaces.

Further reading

  • European Centre for Disease Prevention and Control - an agency of the European Union has published guidance entitled ‘Transmission of COVID-19'.

Epidemiology of COVID-19

When a new infectious disease is discovered, scientists called epidemiologists work with other scientists to find

  • who has it
  • why they have it
  • and what can be done about it
    • how to protect against infections
    • how to supress it before it spreads.

Sources include the US Center for Disease Control CDC and the UK Government website.

COVID-19 Mechanism of transmission

Coronavirus exists inside a host person, and for a limited time, in the area immediately around that host. As the host breathes, the virus is expelled into the air and on surfaces, which they touch or send aerosols to land on.

Coronavirus is carried into a building by an infected person, who will transmit it into the airstreams inside a building by breathing, coughing and/or sneezing. The air inside the building is, therefore, carrying droplets and aerosols which contain COVID-19, which will infect others, if they breath it in. Some of these droplets and aerosols will fall onto surfaces, which then become a transmission risk. And a COVID-19 host will touch surfaces and increase transmission spread through that route.

Airborne transmission

A recent paper published in the Journal of Fluid Mechanics in November 2020, by the Department of Applied Mathematics and Theoretical Physics and the Department of Engineering, University of Cambridge, provides the most up to date view of the effects of ventilation on the indoor spread of COVID-19.

The paper reports that, although the relative importance of airborne transmission of the SARS-CoV-2 virus is controversial, increasing evidence suggests that understanding airflows is important for estimation of the risk of contracting COVID-19. The data available so far indicate that indoor transmission of the virus far outstrips outdoor transmission, possibly due to longer exposure times and the decreased turbulence levels (and therefore dispersion) found indoors. The paper discusses the role of building ventilation on the possible pathways of airborne particles and examine the fluid mechanics of the processes involved

Lessening the risk of transmission

At the current time there is no known medical cure against COVID-19, by vaccine or other physiological means. Therefore, the advice being given by PHE is to:

  • lessen risk
  • avoid inhaling/exhaling in any air which might happen to contain the virus by wearing a mask<
  • follow government guidelines on social distancing and hand washing.

In addition, a range of engineered infection controls can be applied to reduce risks and these are described in this manual.

COVID is a pandemic

Whilst it would be ideal to prevent COVID-19 from entering a country, it has become clear that is very difficult to achieve, particularly in modern times with so much international travel for business or leisure.

The World Health Organisation (WHO) have been monitoring its spread across the world and have declared COVID-19 a pandemic because it is affecting many countries.

Worldometer’ is an organisation which presents data and is a provider of global COVID-19 statistics for many caring people around the world. Worldomoter data is trusted and used by many organisations including:

UK Government | Johns Hopkins CSSE | Government of Thailand  | Government of Pakistan | Government of Thailand | Government of Sri Lanka  | Government of Vietnam | Financial Times | The New York Times | Business Insider | BBC.

COVID-19 figures are reported in terms of cases, deaths, critical cases, recovering cases etc in the Worldometer which is reset after midnight GMT+0.

Worldometer reports that COVID-19 has entered 215 countries and territories round the world and two international conveyances as of 26 October 2020. 

The list of countries and territories and their continental regional classification is based on the United Nations Geoscheme. Sources are provided under "Latest Updates"

Worldometer's figures make it clear that COVID has managed to cross borders into almost all countries despite attempts to block it.

Research to identify routes of transmission have shown the relevant strategies to deal with surface and airborne.

Research has also studied the risks associated with each, such as University of Nebraska work on Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1, published in the New England journal of Medicine, April 2020. This paper gives time scales for survival of virus on different materials as well as in the air. It followed earlier work on viral transmission reported at Antiviral Research in May 2016, 129:21-38. doi: 10.1016/j.antiviral.2016.01.012. Epub 2016 Feb 9.

Mitigating measures with application of engineering

Meeting report: 4th ISIRV antiviral group conference: Novel antiviral therapies for influenza and other respiratory viruses, Jennifer L McKimm-BreschkinAlicia M Fry.

An engineered approach to COVID risk reduction should identify stages where COVID can be stopped or reduced.

Five stages of infection control

Once COVID-19 gets into a country or a community in a country, it is necessary to take steps to limit its spread. This generally means preventing it spreading from one infected person to others.

The general principle is that COVID-19 ‘walks’ into a community within its host person. Control measures must focus onto the interactions between the host and others.

Stage 1: At the source

Commencing at the source, i.e. the face, COVID spread can be limited by simple measures of 'personal infection control' (PIC):

  • Wearing a suitable mask – see Section 5  Transmissions and masks – can limit spread of droplets and aerosols
  • Maintaining ‘social distances’ between people, which means keeping more than 2m apart
  • Washing /disinfecting hands to limit spread of COVID particles on surfaces.
  • The UK Government website provides detailed advice and summarises this approach as 'Wash hands, cover face, make space'.

Stage 2: In high risk areas

    Where there is a risk of meeting a person with COVID such as:

    • Restaurants and bars
    • theatres
    • sports centres
    • shops and supermarkets
    • transport
    • care homes
    • workplaces
    • using infection control and risk management techniques and equipment, implemented/installed with the assistance of engineers.

    These range from barriers, screens and air cleaners such as UV sterilisers and HEPA filters. Effective ventilation is essential.


Stage 3: In communities

    By more costly and widespread public health measures such as:

    • lockdowns
    • self-isolation and quarantine

which impose restrictions on movement and activities. Such measures impose limitations on the normal way of life and impact on businesses, so are only used when necessary.

Stage 4: Following infection through Track-and-Trace

Stage 5: Design for living with COVID-19

COVID-19 has exposed weaknesses in our modern way of life toward contagious pathogens. We live with an assumption that the world is clean and if an infection occurs, we can rely on antibiotics or other methods to deal with it. However COVID-19 has reminded us that nature is continually developing new strains and in the case of COVID they can be very infectious and harmful – and have no cure!

Research into vaccines is underway; however, it takes time and investment to develop new vaccines safely.

We can and should design to live with such risks, for example by using card payments or using proximity readers rather than cash: this reduces transmission of pathogens. However, there are many and much larger engineering solutions.

In construction, we can build with safety and health in mind. Chicago's Fulton East tower is billed as one of the nation's first post-COVID-19 structures designed with enhanced air filtration, widely-spaced offices, and other touchless features.

Within buildings we can apply engineering to achieve safe and healthy occupancy using techniques such as air disinfection.  Equipment such as UV air sterilisation is moving from occasional use to widespread application.

COVID-19 Task Force


Francis Mills


COVID-19 Task Force

  • Get involved with the work of the Committee
  • Share engineering information in the fight against Coronavirus/COVID-19
The new Engineer 360

COVID-19 engineering

Fighting coronavirus - appeals for help, volunteering opportunities and news updates.  
One Birdcage Walk

Reopening from Lockdown - our safety measures 

As our headquarters building and offices reopen, learn how we are working to keep our staff and visitors safe.