Module 102 – Academic Skills
Discuss the reasons why Covid-19 quickly became a pandemic
Covid-19 is a respiratory illness caused by a novel coronavirus: severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2) [1]. Evidence suggests that the virus has a zoonotic origin – specifically
bats – due to the virus sharing an 80% similar genetic sequence with SARS-CoV as well as having
50% genetic sequence similarity to MERS-CoV, which are both coronavirus strains which originated
in bats [2]. The first cases of Covid-19 were reported in Wuhan, China, in December 2019. The virus
spread quickly to other countries due to Wuhan being one of the largest transport hubs in China.
On 11th March 2020, the World Health Organisation declared the outbreak of Covid-19 as a
pandemic [3]. The SARS-CoV-2 virus is passed on by human-to-human transmission of respiratory
droplets, aerosols and fomites, which target the lung epithelial cells primarily. Symptoms of the
virus include a high temperature, continuous cough and fatigue [4]. However, many people who
have the virus are asymptomatic. Both the transmission method and the asymptomatic nature of
the virus could be considered critical factors as to why the virus became a pandemic so quickly. As
of 17th October 2020, there have been over 39 million cases of Covid-19 reported across the world
[5].
People who have Covid-19 can be asymptomatic
One factor that could be considered a crucial reason as to why the Covid-19 virus spread so quickly
is because not everyone who has the virus always develops symptoms. This is known as being
asymptomatic. This feature of the virus has helped it to rapidly spread as people are unaware that
they have the virus, so they do not carry out any self-isolation measures to reduce the spread. This
means they can pass on the virus unknowingly to people whom they come into close contact with.
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A recent study was carried out in which 279 people who tested positive for Covid-19 were
identified and hospitalised. Out of the 279 patients, 23% of them were asymptomatic [6].
Other research has been conducted into the asymptomatic nature of the virus using a familial
cluster case of 5 patients, in which the index patient had been to Wuhan and stayed with a relative
who had Covid-19 but returned with no symptoms [7]. Figure 1 shows that patient 3 developed
symptoms three days after coming into contact with the asymptomatic index patient. Patient 1 and
4 also went on to develop symptoms of the virus. All 5 of the patients in the familial cluster
produced positive Covid-19 tests. This evidence supports the idea that the potential asymptomatic
nature of the virus lends itself to fast transmission because, within the space of around eight days,
one person with no symptoms was able to infect four other people with Covid-19.
Figure 1 Familial cluster study. Timeline of exposure to an index patient with Covid-19 in the familial cluster case study.
Reproduced from Zhang et al., Crit Care 2020 [7]
As well as some people being asymptomatic with Covid-19, many others with the virus are
described as pre-symptomatic. This means that they have the Covid-19 virus but are not showing
symptoms yet. However, they will eventually go on to develop symptoms. The reason that a large
majority of people with Covid-19 are pre-symptomatic is that the virus has an incubation period;
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this is estimated to be 5.1 days. However, for some people, the incubation period can vary from 2
to 14 days [8]. During the incubation period, the virus is rapidly dividing meaning that someone with
Covid-19 is still contagious during the incubation period even though they are pre-symptomatic.
Those who are pre-symptomatic with Covid-19 are rapid transmitters of the virus in the same way
as those who are asymptomatic. This is because they are unaware they have the virus so carry on as
usual without implementing any self-isolation methods. By the time they start to develop
symptoms, it is likely the virus has already been transmitted to multiple people. Both the
asymptomatic and pre-symptomatic potential of the SARS-CoV-2 virus could be considered key
reasons as to why Covid-19 became a pandemic so quickly.
Transmission of SARS-Cov-2
Another prime factor that could be linked to the quick spread of Covid-19 is the way in which the
SARS-CoV-2 virus is transmitted. SARS-CoV-2 is spread by human to human transmission via
respiratory droplets, aerosols and fomites [9]. Infected droplets and aerosols are created when
somebody who is contagious with Covid-19 coughs, talks or sneezes. Droplets and aerosols differ in
particle size, with droplets being bigger particles than aerosols. Anyone who is in close contact with
a person who expels the infected particles will then be at risk of ingesting these potentially
infectious droplets through the orifices on their face. Some of these droplets are not taken in by
anybody but instead fall onto nearby surfaces – fomites [10]. Anyone who then touches these
infected surfaces is at risk of getting Covid-19 by self-inoculation. Self-inoculation can then occur by
methods such as poor hand hygiene. Both of these direct and indirect modes of transmission mean
that Covid-19 can be contracted in an extensive range of everyday environments such as public
transport, healthcare environment and work meetings. This could be viewed as one of the
fundamental reasons as to why Covid-19 became a pandemic so quickly. Given the fast-paced
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world, we live in today people can be in many potentially infectious environments in one day.
Furthermore, the transmission of Covid-19 by indirect contact with contaminated surfaces allows
the virus to infect large numbers of people from a single source, as multiple people are likely to
touch the surface even if they have not been in contacted with the contaminated individual. This
further increases the rate of the spread of Covid-19.
In addition, research suggests that transmission of Covid-19 is greater in confined environments’
such as aeroplanes. Evidence shows that if one person on board an aircraft is infected with Covid19, then it is likely they will go onto infect between five to ten people. This is because flight cabins
are a densely packed environment, so the droplet and aerosol particles are likely to travel both
forwards (by five seats) and backwards (by one seat). Moreover, the aeroplane cabins have
relatively low humidity and temperature levels which provide the perfect platform for the SARSCoV-2 virus to live for a prolonged period allowing more time for others to come into contact with
the infectious particles [9]. With nearly 2 billion people travelling on commercial planes each year
[11] and public
transport being used more than ever in our interconnected society, the fact that
Covid-19 transmission is greater in confined environments could be one of the factors that led to it
becoming a pandemic so fast.
Government Strategies
On 23rd January 2020, the Chinese government imposed a travel ban on Wuhan, stopping all travel
in and out of the city. However, this ban was imposed too late because, as Figure 2 shows, by the
time it had been implemented Covid-19 had already spread to 262 cities in China in just 28 days [12].
This delayed intervention by the Chinese government could be viewed as a significant reason as to
why Covid-19 became a pandemic so quickly. This is because Wuhan is the largest transport hub in
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China, meaning that many people from all over the globe travel in and out of the city regularly.
Between 11th January 2020 and the date of the ban, 4.3 million people were recorded travelling out
of the city of Wuhan [12]. Due to people being asymptotic and pre-symptomatic with the virus it is
likely most people travelling in and out of Wuhan during this time did not realise they had the
Covid-19 virus potentially leading to the rapid transmission of Covid-19 in areas outside of the city.
Many argue that if the Chinese government had reacted more quickly then potentially, they could
have stemmed the fast spread of Covid-19 as people would not have been able to leave the city and
spread the virus.
Figure 2 Covid-19 cases in cities in China The number of cities reporting cases of Covid-19 from early December to 19th February (dotted
line indicates the date of the travel ban in Wuhan). Reproduced from Tian et al., Science 2020 [12]
Furthermore, many other countries governments were also delayed in their responses to the Covid19 outbreak affecting the rate at which Covid-19 was able to spread. For example, in the United
Kingdom face coverings were not made mandatory in public areas until 24th July 2020 even though
evidence had been produced to support the fact that wearing a face-covering reduces the
transmission rate of the virus. Evidence from one study suggests that a cotton mask can block 96%
of viral load [13]. Face coverings are able to reduce transmission because they limit the expelling and
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ingesting of infectious particles. It could be suggested that perhaps if governments had acted
quicker in providing methods to slow the spread of the virus, such as the wearing of face coverings
and lockdowns, then perhaps Covid-19 would not have spread so quickly.
Conclusion
In March 2020 Covid-19 was declared a pandemic due to how quickly the virus was spreading
across the world. Many factors aided in the rapid growth of the virus. How Covid-19 is transmitted
lends itself to naturally fast transmission as well as many people being asymptomatic, allowing
them to be silent transmitters of the SARS-CoV-2 virus. However, the rapid spread of Covid-19 is
not solely due to biological factors; social factors, such as lack of sufficient and early government
intervention, set the permissive conditions for Covid-19 to become a pandemic so quickly.
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