Let us know you agree to cookies
We use cookies to give you the best online experience. Please let us know if you agree to all of thesecookies.

Yes, I agree
No, take me to settings
HomeNewsMoreMenu
HealthCovid: Why is coronavirus such a threat?
By James Gallagher
Health and science correspondent
22 October 2020

Coronavirus pandemic

GETTY IMAGES

A simple virus has brought life as we know it to a screeching halt.
We have faced viral threats before, including pandemics, yet the world does
not shut down for every new infection or flu season

not shut down for every new infection or flu season.
So what is it about this coronavirus? What are the quirks of its biology thatpose a unique threat to our bodies and our lives?

Master of deception
In the early stages of an infection the virus is able to deceive the body.
Coronavirus can be running rampant in our lungs and airways and yet ourimmune system thinks everything is a-ok.

"This virus is brilliant, it allows you to have a viral factory in your nose and feelcompletely well," says Prof Paul Lehner from the University of Cambridge.
Our body's cells start releasing chemicals - called interferons - once they arebeing hijacked by a virus and this is a warning signal to the rest of the bodyand the immune system.
But the coronavirus has an "amazing capability" of switching off this chemical
warning, Prof Lehner says, "it does it so well you don't even know you're ill".
He says when you look at infected cells in the laboratory you cannot tell they
have been infected and yet tests show they are "screaming with virus" and thisis just one of the "joker cards" the virus can play.

It behaves like a 'hit and run' killer
The amount of virus in our body begins to peak the day before we begin to getsick.
But it takes at least a week before Covid progresses to the point where people
need hospital treatment.
"This is a really brilliant evolutionary tactic - you don't go to bed, you go out
and have a good time," says Prof Lehner.
So the virus is like a dangerous driver fleeing the scene - the virus has moved
on to the next victim long before we either recover or die.
In stark terms, "the virus doesn't care" if you die, says Prof Lehner, "this is a hit
and run virus".
This is a massive contrast with the original Sars-coronavirus, back in 2002. Itwas most infectious days after people became ill, so they were easy to isolate.

GETTY IMAGES

It's new, so our bodies are unprepared
Remember the last pandemic? In 2009 there were huge fears about H1N1,
aka swine flu.
However, it turned out to be no way near as deadly as anticipated because
older people already had some protection. The new strain was similar enoughto some that had been encountered in the past.
There are four other human coronaviruses, which cause common coldsymptoms.
Prof Tracy Hussell from the University of Manchester, said: "This is a new one,so we don't think there's much prior immunity there."
The newness of Sars-CoV-2, to give it the official name, she says, can be "quitea shock to your immune system".
This lack of prior-protection is comparable to when Europeans took smallpox
with them to the New World, with deadly consequences.
Building an immune defence from scratch is a real problem for older people,
as their immune system is slow off the mark.
Learning to fight a new infection involves a lot of trial and error from theimmune system.
But in older age we produce a less diverse pool of T-cells - a core componentof the immune system - so it is harder to find ones that can defend against
Coronavirus.

It does peculiar and unexpected things to the body
Covid starts off as a lung disease (even there it does strange and unusualthings) and can affect the whole body.
Prof Mauro Giacca, from King's College London, says many aspects of Covid
are "unique" to the disease, indeed "it is different from any other common viraldisease".
He says the virus does more than simply kill lung cells, it corrupts them too.
Cells have been seen fusing together into massive and malfunctioning cells called syncytia - that seem to stick around.
And Prof Giacca says you can have "complete regeneration" of the lungs after
severe flu, but "this does not happen" with Covid.
"It is quite a peculiar infection," he said.
Blood clotting also goes strangely awry in Covid, with stories of doctors
unable to get a line into a patient because it is immediately blocked withclotted blood.
Clotting chemicals in the blood are "200%, 300%, 400% higher" than normal
in some Covid patients, says Prof Beverly Hunt from King's College London.
She told Inside Health: "Quite honestly, in a very long career, I've never seen
any group of patients with such sticky blood."
These whole-body effects could be due to the cellular doorway the virus
strolls through to infect our cells - called the ACE2 receptor. It is foundthroughout the body including in blood vessels, the liver and kidneys, as wellas the lungs.
The virus can cause runaway inflammation in some patients, making theimmune system go into overdrive, with damaging consequences for the rest of
the body.

And we're fatter than we should be
Covid is worse if you are obese, as a generous waistline increases the risk ofneeding intensive care, or death.
This is unusual.
"Its very strong association with obesity is something we haven't seen withother viral infections. With other lung injuries, obese people often do betterrather than worse," said Prof Sir Stephen O'Rahilly, from the University ofCambridge.

g"It looks pretty specific [to Covid] it probably happens in pandemic flu, but not
regular flu."
Fat deposited throughout the body, in organs like the liver, causes a metabolic
disturbance which seems to combine badly with coronavirus.
Obese patients are more likely to have higher levels of inflammation in thebody and proteins that can lead to clotting.
James Gallagher is a BBC Health and science correspondent in London. He isalso the presenter of Radio 4's The Second Genome and The Inflamed Mind.
Follow James on Twitter

More on this story

Have I got Covid, a bad cold or something else?
5 April

How can I tell if I've got Covid?
6 October 2021

How could artificial antibodies fight coronavirus?
14 September 2020

Related Topics
Medical research

James Gallagher

Coronavirus pandemic

Immune system

Top Stories
LIVE Hundreds still in Mariupol steelworks as Russia resumes attacks
This is your finest hour, Johnson to tell Ukraine
2 hours ago

Missing or dead? Women wait to hear from vanished loved ones
6 hours ago