Context: Though not different from influenza viruses and  other coronaviruses responsible for the common cold, COVID-19 has affected over 1.5 million globally and killed more than 100,000 people, showing the immune system has a predictable response.

How does the virus enter?

  • The viral particles enter the body through the nose, eyes or mouth
    • Breathing carries some of these particles to the lower respiratory tract where the spike proteins of the coronavirus, acting like a key, lock into epithelial cells that line the respiratory tract as well as those in the air sacs in the lungs.
  • Remains undetected: SARS-CoV-2 is able to stay undetected longer than many flu or coronaviruses and its spike proteins are able to gain entry by unlocking the ACE2 protein on the lung cells. 
  • Viruses hijack the cell’s machinery, replicate and multiply and infect adjoining cells. 

How does the immune system respond to a coronavirus attack?

  • Since COVID-19 is not different from influenza virus  and therefore the immune system has predictable responses. 
  • It is the degree to which this response is tolerated by the body that determines mortality rates.
  • Viruses too have a tell-tale signature on their surface called antigens and spotting these is what kicks the immune system into action by producing antibodies.
  • Activating the immune system: The signals they generate trigger another class of chemicals — cytokines and chemokines — and they alert the immune system to send an array of different kinds of cells that specialise in destroying viral particles. 
    • These cytokines and chemokines trigger inflammation in the cells. 
  • In the nose and upper regions of the respiratory system, this inflammation produces mucus and a runny nose to trap viral particles and prevent their ingress. 
    • It also triggers sneezes to expel them. 
    • When the sinuses are inflamed the infected person gets a headache and the general stuffiness that is associated with a cold.
  • When the hypothalamus gland is infected, it results in fever.

How SARS CoV2 is different?

  • In the case of SARS CoV2, the virus seems better at penetrating deeper. 
  • The inflammation triggers a fluid build-up in the lungs. The fluids also contain the residue of a host of specialised cells - including T cells - that carpet bomb and damage many of the body’s own cells as well as the viral particles.
  • It is in expelling this fluid that a dry cough, characteristic of the coronavirus infection, begins. 
  • As more air sacs are infected, the lungs find it harder to perform their core job of extracting oxygen from the air, and eventually, this aggravates breathlessness.


  • Based on degree of infection: The inflammation and the fluid build-up can lead to pneumonia. 
    • A patient will require hospitalisation to treat the breathlessness and ventilator support to artificially provide oxygen if the condition worsens. 
  • Damaging the vital organs: Massive levels of cytokines can cause extensive lung damage and a condition called Acute Respiratory Distress Syndrome. The unsustainable cytokine storm can cause organ damage far beyond the lungs and spread to the kidneys as well as the heart. 
  • In case of acute infection: It will lead to a depletion of the frontline white blood corpuscles tasked with fighting the infection and making the body vulnerable to other secondary infections, which may lead to death.

Immune system response:


  • Weak immune system: those with existing conditions such as diabetes and cardiovascular disease, already have an inherent malfunctioning in the immune system.
  • The reaction of the body in trying to combat the virus ends up being suicidal.
  • Hydroxychloroquine or anti-HIV drugs, deployed to treat serious COVID-19 infection work in some way to moderate the immune-system’s aggressive defence.


Men are twice more likely than women to succumb to a COVID-19 infection:

  • Women, on average, have a better-regulated immune response than men in pathogenic infections.
  • Estrogen is said to be an immune-system modulator and the ability to deal with a pregnancy - which also begins as a foreign body growing within - primes women to better deal with infections.


  • Not very clear: so far, there have been few deaths reported in children from COVID-19. Given that children’s immunity systems are still maturing and learning to adapt to a galaxy of infectious agents.


Image Source: Everyday health