COVID-19 is more dangerous than flu viruses 

While COVID-19 and flu viruses are thought to spread in similar ways, COVID-19 is more dangerous than flu viruses because it:

Is more contagious than flu among certain populations and age groups

• What is disturbing is that virus shedding, as detected in the mouth or nose, is very, very common and could be there prior to onset of symptoms.

Is more stable and can survive a longer time

• At 68 ℉, COVID-19 can survive on banknotes, glass and stainless steel for up to 28 days, much longer than the flu virus which is 17 days

• Proteins and fats in body fluids can also sharply increase Covid survival times

  • This helps to explain the apparent persistence and spread of SARS-CoV-2 in cool environments with high lipid or protein contamination, such as meat processing facilities

Potentially Dangerous for All People

What are the quirks of its biology that pose a unique threat to our bodies and our lives? 

Is a master of deception

• Our body's cells start releasing chemicals - called interferons - once they are being hijacked by a virus and this is a warning signal to the rest of the body and the immune system.

• But the coronavirus has an "amazing capability" of switching off this chemical warning, it does it so well you don't even know you're ill.

Is a 'hit and run' killer

• The virus doesn't care if you die, this is a hit and run virus.

  • 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.

• The amount of virus in our body begins to peak the day before we begin to get sick.

  • But it takes at least a week before Covid progresses to the point where people need hospital treatment.

Does peculiar and unexpected things to the body

• Covid starts off as a lung disease (even there it does strange and unusual things) and can affect the whole body

  • 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 found throughout the body including in blood vessels, the liver and kidneys, as well as the lungs.

  • Covid 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.

• Blood clotting also goes strangely awry in Covid

  • Clotting chemicals in the blood are "200%, 300%, 400% higher" than normal in some Covid patients

    • Doctors sometimes were unable to get a line into a patient because it is immediately blocked with clotted blood.

• Covid can cause runaway inflammation in some patients, making the immune system go into overdrive, with damaging consequences for the rest of the body

Why Coronavirus is more dangerous for older people?

Different from other coronavirus, this virus is a new one, we don't think there's much prior immunity in any groups including older people.  

Building an immune defense from scratch is a real problem for older people (note that biological aging, as captured by PhenoAge, is a better predictor of COVID-19 severity than chronological age [13]) because: 

• Their immune system is slow off the mark

  • Learning to fight a new infection involves a lot of trial and error from the immune system

• They produce a less diverse pool of T-cells

  • So it is harder to find ones that can defend against Coronavirus.

In addition,  hospitalized older COVID-19 patients had elevated levels of pro-inflammatory markers, which including:[14]

• Neutrophil-lymphocyte ratio, D-dimer, C-reactive peptide and certain cytokines (i.e., IL-8 and IL-27)

Based on another publication, here are the reasons why children fare better than adults:

The expression of primary target receptor for SARS-CoV-2, i.e. angiotensin converting enzyme-2 (ACE-2), decreases with age. ACE-2 has lung protective effects by limiting angiotensin-2 mediated pulmonary capillary leak and inflammation. Severe COVID-19 disease is associated with high and persistent viral loads in adults. 

Children have strong innate immune response due to trained immunity (secondary to live-vaccines and frequent viral infections), leading to probably early control of infection at the site of entry. Adult patients show suppressed adaptive immunity and dysfunctional over-active innate immune response in severe infections, which is not seen in children. These could be related to immune-senescence in elderly.

Room for Hope?

But there is room for hope as the world attempts to stave off a bitter Covid-19 winter. Mortality rates from the virus have fallen over the course of the year as healthcare expertise and technology have improved. 

In March, somebody aged 70 or above had a 50:50 chance of survival if admitted to hospital with the virus. By August their chances had climbed to 74 per cent. 

References

1. Covid: Why is coronavirus so deadly?

2. Even Mild Covid-19 Infections Can Make People Sick for Months

3. As evidence builds that COVID-19 can damage the heart, doctors are racing to understand it

4. A perspective on potential antibody-dependent enhancement of SARS-CoV-2

5. COVID-19 survivors suffer long term heart conditions

6. Your Risk of Getting Sick From Covid-19 May Lie in Your Genes

7. Male coronavirus patients with low testosterone levels are MORE likely to die from COVID-19, German hospital finds

8. Covid Doctors Find a Turning Point in Life-Threatening Cases

9. Strokes and mental state changes hint at how COVID-19 harms the brain

10. Death Rate of Covid-19 by Age / Prior Illness / Ethnic Group

11. Covid-19: The global crisis — in data

12. Common cold antibodies hold clues to COVID-19 behavior

13. COVID-19 severity is predicted by earlier evidence of accelerated aging

14. Investigating Age Differences in COVID-19 Immune Response