How is COVID-19 Spread?

COVID-19 is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is primarily spread person to person by small droplets, or by contacting contaminated surfaces. Maintaining social distancing and maximizing personal hygiene levels reduces the risk of transmitting the virus, as well as reducing your risk of getting infected.

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What is COVID-19?

Coronavirus Disease 2019, or COVID-19, is an infectious acute respiratory disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Initially identified in Wuhan, China, COVID-19 rapidly became a global pandemic as of 30^th January 2020 and is still ongoing. Worldwide, around 8 million cases of COVID-19 have been confirmed with around 450,000 deaths (as of June 2020).

Symptoms of COVID-19 vary person to person but typically include flu-like symptoms that appear within 2 days after infection (see here for COVID-19 symptoms). An infected person is usually contagious for up to 14 days and based on this, affected individuals must self-isolate for 2 weeks until symptoms disappear.

For a minority of patients; usually over the 70s and those with pre-existing health conditions, the symptoms may worsen and require hospitalization.

As COVID-19 is a new disease, the exact mechanisms and transmission routes are still become apparent. However, it is now well established that affected people are at their most infectious (contagious) upon showing initial symptoms and can remain contagious for up to 12-14 days.

A small proportion of affected individuals may be completely asymptomatic and can still be contagious nearby, though most people will only be contagious as long as symptoms persist.

How is COVID-19 Spread?

As COVID-19 belongs to the coronavirus family – closely related to the SARS & MERS virus – the primary route of transmission is the inhalation of small respiratory droplets from an infected person.

These small droplets produced from an infected person (symptomatic or asymptomatic) usually arise from sneezing, coughing, and even talking. Thus, those within proximity of less than 1 meter from an infected person at a high risk of inhaling viral particles from an infected person.

Larger respiratory droplets (talking and coughing mildly) only remain in the air for a short period and typically do not travel distances greater than 1 meter. However, smaller respiratory ‘nuclei’ from sneezing (aerosolized) can travel distances greater than 1m.

The current evidence suggests that in most cases COVID-19 is transmitted by respiratory droplets, though symptomatic individuals that sneeze (less common in COVID-19 than flu) can propel particles much further. Thus, the risk of infection inside enclosed spaces is greater than being outside.

Other indirect routes of transmission may include coming into contact with contaminated surfaces as a result of contagious droplets falling on surfaces, such as door handles for example. When someone touches an infected surface and then touches their face (close proximity to mouth, nose, and eyes), the risk of the virus entering the body is significantly increased.

Coronaviruses, in general, have poor survivability on surfaces thus the risk of getting infected by touching parcels or shopping items is relatively low (the virus can only survive up to 1 day on cardboard and up to 2 days on plastic).

If in doubt, or you have bought something from a busy shop, it may be advisable to wipe surfaces with a detergent disinfectant or alcohol wipes. Takeaway deliveries are deemed safe due to enhanced hygiene efforts in a majority of restaurants and takeaways, and the risk of surface contamination is very low.

Lastly, some evidence has suggested the presence of SARS-CoV-2 RNA in stool samples from infected people – though whether these are infectious virus particles is still to be seen. Some evidence does point to infectious viral particles being present after flushing the toilet and keeping the toilet lid down reduced this supposed spread.

It is also safe to assume, based on all the emerging evidence, that all bodily secretions except for sweat may contain infectious virus particles. However, none of these routes are thought to be the main infectious route for SARS-CoV-2, although caution is advised.

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Preventing COVID-19 Spread

In line with WHO guidelines, and national guidelines (e.g. NHS for the UK, CDC for the US), all those with symptoms of COVID-19 (or any new ‘flu’-like symptoms) should immediately self-isolate (or quarantine) for 14 days after symptoms develop.

During this time, infected (or suspected) individuals must not leave the house, except for essential purposes such as exercise. Shopping should be done by a family or friend on their behalf, if possible. Wherever an infected person chooses to leave their house, they must remain socially distant and wear a face covering at all times.

The WHO recommends a 1-meter social distancing rule in all settings (apart from those within the same household, or those forming exclusive social bubbles), however, the UK government recommends a 2m distance rule (6 feet) – though this is under review currently to be reduced to 1m to allow small businesses such as pubs and restaurants to reopen.

The evidence for using face masks or coverings was initially ambiguous, however, evidence has strongly pointed to the use of face coverings in public places to prevent spread. Many countries now legally require people to wear face coverings in public places, including transport.

Face coverings may include scarves, homemade coverings from t-shirts, etc, or proper masks. Wearing a covering greatly reduces the risk of transmitting the virus. However, healthcare workers, children under 2 years, or those with conditions such as asthma should not wear a face covering.

Washing one’s hands for 20 seconds with hot water and soap is an effective way to eliminate virus particles on one’s hands and should be performed more regularly than usual. Washing should be done especially after returning home after shopping, for example, or in an office or retail environment where there are shared facilities.

Hand sanitizers with a minimum of 60% alcohol content are also effective and should be used when washing is not possible. Furthermore, people should avoid touching their face with unwashed hands.

Preventative strategies as the ones discussed above, in addition to government policies and adherence to such strategies, are crucial in bringing down the R₀ for COVID-19 within a location until a vaccine and cures are developed. Only with limiting R₀ (less than 1) can local epidemics and the global pandemic be over.

Future flare-ups may occur with a resurgence of a second wave in the winter months, and until a vaccine is developed, only by actively preventing spread, can the R₀ be limited to 1 or lower thus preventing an epidemic again.

In summary, COVID-19 is primarily transmitted through respiratory droplets from an infected person – such as by sneezing, coughing, or talking – and contagiousness is usually limited to the duration symptoms persist. Respiratory droplets may persist on surfaces for a day or two and contacting contaminated surfaces and touching one’s face may also indirectly lead to infection.

Wearing face coverings, washing hands regularly, self-isolating if symptomatic, and maintaining a social distance of at least 1 meter is essential to limiting the spread and in combatting the pandemic (and regional epidemics).

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Further Reading

• All Coronavirus Disease COVID-19 Content
• What Mutations of SARS-CoV-2 are Causing Concern?
• What is the Clinical Impact of COVID-19 on Cancer Patients?
• Can Pets Get COVID-19?
• An Overview of the SARS-CoV-2 Vaccines

Written by

Osman Shabir

Osman is a Neuroscience PhD Research Student at the University of Sheffield studying the impact of cardiovascular disease and Alzheimer's disease on neurovascular coupling using pre-clinical models and neuroimaging techniques.