Coronavirus spreads by droplets from the mouth and nose and you can pick it up by touching someone who is infected (for example, shaking hands), by touching a contaminated surface or by breathing in an infected person’s respiratory secretions. But what does it actually do to you once entering the body?

Watch the above video featuring easy to understand animations and explanation from our Global Health Security Editor Paul Nuki to find out. And read on below for a detailed written account of the disease.

So what does it do?

For the vast majority of people – more than 80 per cent – the virus will cause only mild symptoms and pass like a common cold. But data from China show that about 14 per cent of cases are severe and five per cent are critical, with patients ending up in intensive care, needing help with breathing. 

The death rate is somewhere between two and four per cent in Wuhan, the epicentre of the outbreak in China, but less than one per cent in the rest of China and the world. 

The higher death rate in Wuhan is not clearly understood but experts believe it is down to a range of factors: only the most severe cases were picked up at the beginning of the outbreak; doctors and nurses were slow recognise the new disease; and health services were overwhelmed, meaning patients did not get the best care. 

What happens when the virus enters the body?

When the virus enters your body it binds to two cells in the lungs – goblet cells that produce mucus and cilia cells which have hairs on them and normally prevent your lungs filling up with debris and fluid such as virus and bacteria and particles of dust and pollen.

The virus attacks these cells and starts to kill them – so your lungs begin to fill with fluid making it hard for you to breathe. This phase of the disease is thought to last about a week. 

At this point your immune system will start to kick in and fight off the invaders. You will develop a fever and your high body temperature will create a hostile environment for the virus. You will start to get rid of the mucus in the form of coughing and a runny nose. 

But in some people – particularly the elderly and those with other health conditions – the immune system can go into overdrive. As well as killing the virus it also starts to kill healthy cells. 

This heightened immune response can trigger a “cytokine storm” – white blood cells activate a variety of chemicals that can leak into the lungs, which along with the attack on the cells damages them even further. Scans of the lungs show “ground-glass” opacity and then “crazy paving” patterns, as they fill with mucus making it harder and harder to breathe. 

Bacterial infections can also take hold at this point and your weakened immune system will struggle to fight them off. 

This heightened immune response can lead to organ failure and death. It was a common cause of mortality in the Spanish Flu of 1918. 

Some people who recovered from severe acute respiratory syndrome (Sars) which swept the world in 2002 to 2003 had long-term respiratory problems as their lungs were permanently damaged. Covid-19 is similar to Sars in some respects, although is much less lethal, so those who have recovered from more serious symptoms may also suffer some long-term effects. 

While people with weakened immune systems and the elderly are more likely to become critically ill the younger and healthy in China and elsewhere have also succumbed to the virus – this is because none of us have any immunity to this new disease.

However, one interesting factor is that children do not seem to be falling victim to Covid-19 – just 2.4 per cent of all those who have contracted the disease are 18 and under and the vast majority have mild symptoms. In other respiratory diseases such as flu children are key disease transmitters. 

It is still unclear whether children are less susceptible to the disease or whether they just have very mild or asymptomatic infections. According to the World Health Organization there has been no confirmed case of an adult picking up Covid-19 from a child. 

How to stay safe

The single best thing you can do to stop the virus is to wash your hands frequently and thoroughly – particularly before you eat.

Face masks can stop you spreading the virus but they are unlikely to prevent you picking it up from someone else. This is because they have to be changed frequently, and removed and disposed of properly. 

The virus is most likely to enter your body from your own contaminated hands when you touch your nose, eyes and mouth. We touch our faces up to around 23 times an hour, studies suggest, and this is the prime route of infection. 

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