COVID-19: Background, Symptoms & Transmission

By Gagandeep Sachdeva

 Disclaimer: The information for the upcoming series of posts on the Coronavirus has been collated from a range of sources and the purpose is to provide insight into the virus from an objective lens. These posts are accurate to the time of publication; however, our knowledge of the virus is rapidly evolving, so we recommend for you to stay up to date with the latest news broadcasts and research.


 The new Coronavirus (COVID-19) has been declared as a global health emergency by the World Health Organisation (WHO), with over 935,000 cases and over 47,000 deaths from across 203 countries and territories as of 12:30pm on 2nd April 2020 (1,2). Multiple organisations have published research on the virus and over a series of posts, we will explore the findings to get you up to date with this outbreak.

This post will explore the scientific details of the virus, the symptoms observed and transmission.

The 2019 Coronavirus disease (COVID-19) is caused by SARS-COV-2, a virus that primarily targets the respiratory epithelium (3). It belongs to a Coronavirus family of single-stranded RNA viruses (4). A Coronavirus pandemic was seen in 2002 (SARS-COV-1), with genomic studies showing an 80% matched genetic identity of this virus with COVID-19 (3). COVID-19 is likely of zoonotic origin, based on the large number of infected people who were exposed to the wet animal market in Wuhan, China. Genetic sequencing has shown 88% resemblance of COVID-19 infecting humans, with the virus in bats, suggesting a potential source and reservoir of the virus (3).

Viruses are obligate intracellular parasites, meaning they must be internalised into host cells to replicate and cause disease. COVID-19 has surface ‘spike-like’ glycoproteins which bind a human cell membrane enzyme (called ACE2) with high affinity, permitting cell entry (5). Viral replication then commences and the increasing viral load exacerbates the disease. Luckily, the body’s immune system is the defense against pathogens, and the foreign viral markers initiate an inflammatory response with the aim to fight off the infection.

The immune system’s response is what produces the symptoms of the disease. In the case of COVID-19, the key symptoms as outlined by NHS UK (6) are:
  • High temperature
  • New, continuous cough: “coughing a lot for more than 1 hour, or 3 coughing episodes in past 24 hours (if usually have a cough, it may be worse than usual)”
  • Other symptoms may include headache, shortness of breath, sputum production and diarrhoea
The virus has been calculated to have approximately a 5-day incubation period (the time from exposure to the virus, to the onset of symptoms), with initially mild symptoms at presentation and progression to pneumonia at day 9 of illness (3). 80% of patients experience mild symptoms, however vulnerable groups including the elderly and those with underlying health conditions, have a risk of severe infection and respiratory compromise which could be fatal. This is evidenced by the unfortunate higher mortality rate from the virus in the elderly population.

The predominant modalities of transmission of COVID-19 are airborne droplets (coughs and sneezes) and contact with infected people and surfaces. The virus is highly contagious, with estimated figures suggesting 1 person on average passes the virus onto 2.2 people. This spread rate is referred to as the R0 value. For context, the seasonal flu has R0 of 1.3, while the deadly Spanish flu of 1918 had an R0 value estimated between 1.4-2.8 (7).

The enforcement of lockdown and quarantine aims to reduce the spread of COV-19. 7-day self-isolation has also been advised by NHS UK if an individual or someone they live with has symptoms of COVID-19. Extension of this self-isolation is advised if the individual still has a high temperature.

We hope that this post has been informative. Please continue to quarantine and strictly follow policies from local authorities and the Government.

 References:  
1. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/events-as-they-happen  
2. https://www.worldometers.info/coronavirus/ 
3. https://www.sciencedirect.com/science/article/pii/S0896841120300469 
4. https://www.ncbi.nlm.nih.gov/books/NBK554776/ 
5. https://cen.acs.org/analytical-chemistry/structural-biology/Structure-novel-coronavirus-spike-protein/98/i8 
6. https://www.nhs.uk/conditions/coronavirus-covid-19/symptoms-and-what-to-do/ 
7. https://www.healthline.com/health/r-nought-reproduction-number#rsubsubvalues 
8. https://www.nhs.uk/conditions/coronavirus-covid-19/self-isolation-advice/ 

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