Immune System vs COVID

About the immune system

The immune system is made up of a collection of specialised cells, biological pathways and chemical processes that function as your body’s guardian, protecting us from unwanted foreign substances such as bacterial, viral, parasitic and fungal infections, cancer cells and harmful toxins. The immune system can be split into two arms, the innate immune system and the acquired immune system. Equally as important for proper defense as they are different, these two arms work in separate synergy to deliver an effective immune response.

The innate immune system is our first line of defense, its acts with an instantaneous, non-specific intent to block and destroy a broad range of foreign pathogens that have entered the body. Upon detecting a foreign invader, this identity is given away a distinguishing marker called an antigen on the surface of the pathogen, and the innate immune system kicks into action. The innate immune system uses a cell-mediated response to kill infected cells and destroy unwanted pathogenic particles and triggers a chemical cascade of inflammation that forces many immune cells to flood towards the infected zone to optimise defense.1 The innate immune also induces the second line of immune defense, the acquired immune system.

The acquired immune system is made up of T and B white blood cells that act in a highly specific manner against the invading pathogen. The acquired immune system constructs an immunological memory.2 During the response to the pathogen it creates and stores antibodies that are specific to the pathogens’ cell surface antigens (distinguishing particles), this process takes 6-8 days after infection. Antibodies stimulate the immune response by flagging up unwanted pathogens and marking them for degradation. Additionally, they can bind to intracellular pathogens like viruses to stop them from entering and infecting healthy host cells. Lastly, antibodies can clump many pathogenic particles together to make them easier to remove all at once. A small number of antibodies forged will be stored in the body for years after the infection. This means they circulate the body ready to bind to the specific pathogen upon reinfection. Therefore, if you contract the same pathogenic infection later down the line, this immunological memory will allow antibodies to recognise the pathogen straight away instead of having to wait around a week for the acquired immune response to begin like before. Less time is taken to create the tailored antigen-specific antibodies because they already exist, and pathogens are flagged up and destroyed quicker. 

What is covid?

Covid-19, or coronavirus, is caused by a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Covid-19 primarily affects the respiratory system, therefore, key symptoms of the infection manifest there. These symptoms vary from patient to patient, ranging from mild to severe, and can appear 2 to 14 days after contraction of the virus. Symptoms include but are not limited to:3

  • A new and persistent cough
  • Loss or change of smell
  • Loss or change of taste
  • Fever (high temperature and shivering)
  • Shortness of breath
  • Sore throat
  • Congestion (blocked or runny nose)
  • Headaches
  • Nausea
  • Diarrhoea
  • Body aches and pains
  • Fatigue (feeling exhausted)
  • Loss of appetite

Covid-19 is spread through virus-containing droplets ejected from the body by sneezing, coughing and talking. These particles then enter the body through the eyes, nose, or mouth, where they travel downwards to reach the lower respiratory tract. Here, the spike protein of the coronavirus is inserted into the lung epithelial cells that line the tract. Acting like a key to a lock, the spike protein allows for the virus to move into the cell. Here covid-19 hijacks the cell's internal machinery to multiply and infect nearby cells.4

Immune system vs covid: how the immune system responds to and fights covid

Our bodies respond to a COVID-19 infection by operating both domains of the immune system, the innate immune system and the acquired immune system.

Like all viruses, covid-19 has a tell-tale marker of its identity on its surface called an antigen, and when this is recognised by cells of the immune system, an anti-viral response is triggered. Cytokines and chemokine chemicals are released which cause inflammation (an innate immune response), these chemicals attract masses of immune cells to the infected area to destroy the cells. Whilst inflammation is needed to increase the immune cell response, Inflammation in the lungs causes the air sacs to fill with fluid reducing the effectiveness of gas exchange. This manifests in the main symptom of covid-19, a persistent cough and trouble breathing. The innate immune response includes anti-viral interferons. Interferons are cytokines that are produced by a cell that has been infected with the virus. Interferons bind to nearby cells to inform them of the infection so that their viral defences are increased, this is an effective mechanism to stop covid-19’s spread through the body.5 Furthermore, natural killer cells are innate immune cells that constantly patrol the body and will kill cells that are infected with a virus. The infected cells will have markers on their surface to show that they are compromised, natural killer cells will bind to this and attack the infected cell, killing it to destroy the virus.6

The acquired immune response is activated by the innate immune response. T helper cells bind to the antigen and activate, T helper cells go on to activate cytotoxic T cells. These cells will specifically detect infected cells by antigen recognition and pierce holes all over the surface of the infected cell. This causes the cell to burst and die, without a vessel, the coronavirus cannot continue so its threat is ameliorated. Activated T helper cells will also go on to activate B cells. B cells will produce two types of antibodies, some to use immediately in pathogen defence and others to store in the event of a secondary infection. The available antibodies will trigger an efficient and specific antiviral response by stopping the lock and key mechanism of covid-19 so that it cannot enter the host lung cells and by flagging up cells for degradation that present the antigen on their surface.7

The stored antibodies secreted by B cell clonal selection will circulate the body, ready to recognise covid-19 should reinfection occur. This immunological memory means that less time is needed to create the tailored antibodies as part of the acquired immune response, increasing the anti-viral immune aggression so that you fight off the virus quicker.8 Vaccines - including the covid-19 vaccines - work with the same principle, a harmless part of the virus importantly with antigens on its surface is injected into the patient to mimic the primary infection and stimulate an immune response without you getting ill. This will create antibodies to protect you should you encounter the virus later on, with the same rapid innate immune response and an even quicker acquired immune response.


How do I reinforce my immune system to fight against covid ?

Getting vaccinated is very important, it gives your body the best possible chance of fighting off covid-19 efficiently upon contracting it. It reinforces your immune system so that it will recognise and destroy the virus when it comes into contact.

Living a healthy lifestyle will optimise the strength of your immune system, this includes:

  • Having a balanced nutritious diet with lots of fruit and vegetables
  • Staying active – getting enough exercise will benefit your pulmonary health
  • Maintaining a healthy weight – obesity is a risk factor for poor covid-19 outcomes
  • Not smoking – Cigarette smoke damages your lung cells making it harder for them to fight off infection and making symptoms much worse.
  • Drinking less alcohol
  • Getting enough sleep – 8 hours is the recommended amount each night
  • Taking care of your mental wellbeing      

Can I get immunity to covid?

Yes, you can get immunity from covid-19. The best example to prove this is the success of the  vaccination program. Once injected with a harmless antigen-containing part of the virus, the body starts making antibodies in response. This means that you will have a faster immune response to a covid infection should you catch it, and symptoms should be less severe and last for less time.

You can get immunity to covid-19 by contracting the virus too. Upon reinfection, the antibodies that remain in the body since the first infection will orchestrate a rapid immune response to the virus.

Both of these types of immunity will not last forever though. That is why it is important to get covid-19 booster vaccinations to "top up" the number of antibodies you have so that your immune recognition capacity for covid-19 is always high.

How will I know if I have a strong or weak immune system?

If you are young, free of any medical ailments and live a healthy lifestyle your immune system should be relatively strong. However, you never know how your body is going to respond to infection so it is important to get vaccinated as soon as you can.

If you have a weakened immune system you will not be able to fight off a covid infection as well as others leading to severe side effects. According to the NHS,9 you are considered clinically vulnerable to severe covid infections if you are:

  • Elderly (aged 60 or over)
  • Pregnant
  • Not vaccinated against COVID-19
  • A person with Down's syndrome
  • A cancer patient (such as a blood cancer like leukaemia or lymphoma)
  • Receiving immunosuppressing treatments including biological therapy, chemotherapy or radiotherapy
  • Living with sickle cell disease
  • A chronic kidney disease patient (stage 4 or 5)
  • A severe liver disease patient
  • A recent recipient of an organ or bone marrow transplant
  • Living with an autoimmune or inflammatory condition (such as rheumatoid arthritis or inflammatory bowel disease)
  • Living with HIV or AIDS
  • Living with a brain or nervous system disease (like multiple sclerosis, motor neurone disease, Huntington’s disease or myasthenia gravis)
  • Someone with severe or multiple learning disabilities

For most vulnerable people, the covid-19 risk is lowered after you receive the vaccines and booster so the best advice if you fall into one of these categories, is to book an appointment to get it. For others, despite the vaccine, the covid-19 risk still remains high. In this case, you should still wear a face covering in public, avoid coming less than 2 meters away from people, try and work from home if you can and regularly wash your hands using soap and water. These steps will help you avoid the infection.

When should I see a doctor? 

For most healthy, young, vaccinated people, your body will be able to fight off COVID-19 on its own and you will be able to manage symptoms from home. However, you should contact your GP or 111 for advice if you are suffering from covid and you are:10

  • Gradually feeling more unwell or more breathless, especially if you still feel unwell after 4 weeks (this may be ‘Long COVID’)
  • Finding it difficult to take care of yourself properly and need support doing day-to-day tasks
  • Having difficulty breathing
  • Feeling very weak and fatigued
  • Losing your appetite

If you have covid, you should seek URGENT medical attention by calling for an ambulance if:

  • You are very breathless or if your breathing difficulties have suddenly increased
  • You cough up blood
  • You collapse or pass out
  • You feel confused or drowsy
  • Your urine production is much less than usual
  • Have a rash that does not fade when you roll a glass over it


With miraculous scientific advances, covid-19’s threat has been reduced, and to many people, it is no longer a death sentence. This is all because vaccines and treatments have been designed with the mechanics of immunity at the forefront. The risk of covid-19 solely is based on a person’s individual immunity which you can boost with the vaccine and a healthy balanced lifestyle. This article was written to increase understanding of the immune system and covid-19’s intimate relationship and encourage you to take your health into your own hands by taking the steps to improve your immunity and stay vigilant towards the virus.


  1. Turvey SE, Broide DH. Innate immunity. Journal of Allergy and Clinical Immunology. 2010 Feb 1;125(2):S24-32.
  2. Bonilla FA, Oettgen HC. Adaptive immunity. Journal of Allergy and Clinical Immunology. 2010 Feb 1;125(2):S33-40.
  3. Struyf T, Deeks JJ, Dinnes J, Takwoingi Y, Davenport C, Leeflang MM, Spijker R, Hooft L, Emperador D, Domen J, Tans A. Signs and symptoms to determine if a patient presenting in primary care or hospital outpatient settings has COVID‐19. Cochrane Database of Systematic Reviews. 2022(5).
  4. Tufan A, Güler AA, Matucci-Cerinic M. COVID-19, immune system response, hyperinflammation and repurposingantirheumatic drugs. Turkish journal of medical sciences. 2020;50(9):620-32.
  5. McNab F, Mayer-Barber K, Sher A, Wack A, O'garra A. Type I interferons in infectious disease. Nature Reviews Immunology. 2015 Feb;15(2):87-103.
  6. Li G, Fan Y, Lai Y, Han T, Li Z, Zhou P, Pan P, Wang W, Hu D, Liu X, Zhang Q. Coronavirus infections and immune responses. Journal of medical virology. 2020 Apr;92(4):424-32.
  7. Chowdhury MA, Hossain N, Kashem MA, Shahid MA, Alam A. Immune response in COVID-19: A review. Journal of infection and public health. 2020 Nov 1;13(11):1619-29.
  8. Rokni M, Ghasemi V, Tavakoli Z. Immune responses and pathogenesis of SARS‐CoV‐2 during an outbreak in Iran: Comparison with SARS and MERS. Reviews in medical virology. 2020 May;30(3):e2107.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

Get our health newsletter

Get daily health and wellness advice from our medical team.
Your privacy is important to us. Any information you provide to this website may be placed by us on our servers. If you do not agree do not provide the information.

Frankie Perrett

MSc Molecular Medicine and BSc Biological Sciences – University of East Anglia, Norwich

Frankie works in an NHS Hospital Pathology laboratory so has acquired excellent insight into many different diseases and their mechanisms of action.

Frankie’s Master’s course focused on key areas of biomedicine, centring around patient-first learning. In her degree, she specialised in Lung adenocarcinoma and its mechanisms of cell communication.

Leave a Reply

Your email address will not be published. Required fields are marked * presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
Klarity is a citizen-centric health data management platform that enables citizens to securely access, control and share their own health data. Klarity Health Library aims to provide clear and evidence-based health and wellness related informative articles. 
Klarity / Managed Self Ltd
Alum House
5 Alum Chine Road
Westbourne Bournemouth BH4 8DT
VAT Number: 362 5758 74
Company Number: 10696687

Phone Number:

 +44 20 3239 9818