UNDERSTANDING COVID-19

With so much information (and misinformation) at our fingertips, we take a moment to outline the facts about COVID-19, what it is and how it compares to seasonal flu. 

Various names are being used in conjunction with the current pandemic, but it’s probably worth confirming the official (and correct) nomenclature. The virus is named SARS-CoV-2 and it causes the disease COVID-19.

The widely used term “corona virus” actually refers to the corona virus group, to which SARS-CoV-2 belongs. These corona viruses get their name from the spiky, crown-like fringe that covers each virus particle (pictured above). Corona viruses tend to target the respiratory systems of mammals (including bats) and birds. They tend to remain specific to their wild hosts but occasionally cross into humans, such as the events that sparked the SARS outbreak in 2003 (the virus was called SARS-CoV) and the MERS outbreak in 2012. Both of these are suspected to have originated in bats, which is why bats are also suggested as a likely origin for SARS-CoV-2.

Comparing COVID-19 and seasonal flu

Comparisons between COVID-19 and seasonal flu are common in the media. This is not surprising in that a lot of the symptoms of the two diseases are similar. However, there are significant differences in the disease epidemiology (disease transfer, effects and control).

Influenza has a shorter incubation period than COVID-19 (three days versus five or six days) so actually has the potential to spread faster than COVID-19. However, for around 80% of COVID-19 infections, the symptoms are mild or non-existent, meaning infected people will be a source of infection without knowing they are a risk. Indeed the reproductive number – the average number of additional people infected from a single infected person – is significantly higher for COVID-19 (currently estimated at R=2.5-3.0) than for seasonal influenza (R=1.28). However, some believe it is a lot higher still and this will only be determined once they are able to test a large percentage of the population.

The virus is spread through close contact, typically within 1.5 to 2 metres. The principle route of infection is through respiratory droplets (for example when someone coughs), which are inhaled or land on the mouths or noses of people nearby. As the virus can remain on surfaces for
at least several hours and maybe up to a couple of days, touching contaminated surfaces and then touching your mouth, nose or eyes could also transfer the virus.

COVID-19 symptoms include a dry cough, sore throat, fever, headaches, body aches and fatigue. Influenza can produce very similar symptoms, although if you start suffering from shortness of breath, that is only a symptom of COVID-19. If you are sneezing you are simply suffering from a common cold or allergy.

There is a key difference in the pathology of the two diseases. Whereas influenza appears to have a big impact on the young and elderly, pregnant women, and those with pre-existing conditions and immune system deficiencies, COVID-19 symptoms seem most severe in the elderly and those with underlying medical conditions. For reasons yet unknown, children rarely seem to be affected by the virus, although the level of infection is unknown. It has also been suggested that children are not a major cause of infection transfer. However, in contrast, it is known that children are a major cause of transfer of influenza.

Globally, as of April 15, the case fatality rate for COVID-19 is around 6% (number of deaths as a percentage of confirmed cases), although the actual mortality rate as a percentage of those infected it is likely to be lower as the number of actual cases will be higher than recorded (many cases will be undetected). In Australia the case fatality rate is much lower at around 1%. As a point of reference, the mortality rate for influenza is lower still, at 0.1%.

It is of course dangerous to talk in percentages. With a highly infectious disease even a low mortality rate translates to a large number of fatal cases. On top of which, the pressure on the health services resulting from the pandemic means that there is no room for the normal intensive care cases (heart attacks, strokes, etc). Without prompt intensive care, the mortality in these normally critical patients would be significant.

It is important to remember that there is no immunity to SARS-CoV-2 in the community as it is a new virus, whereas there is some level of community immunity to the various influenza viruses – and of course a flu vaccine is available. It is the unknown nature of COVID-19 coupled with the lack of vaccine and curative treatment that is driving the policies regarding pandemic management.