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HERD IMMUNITY AND COVID-19

By Dr. Stephen A. Berger

Herd immunity concept. People of different age groups, men, women and children are protected from the harmful effects of viruses. Preventive measures, human protection, group immunity.

WHAT IS HERD IMMUNITY?

It stands to reason that a contagious disease should disappear from a population when a sufficient percentage of potential victims – “the herd” has become immune. This outcome may arise because a massive number of individuals have been either infected or vaccinated.

Most authorities dealing with COVID-19 have set the goal for herd immunity at >60 percent; however, the precise percentage for any infectious disease will depend on many factors involving demography, virulence, route of infection, etc. 

 

HAS AN INFECTIOUS DISEASE EVER BEEN ERADICATED BY REACHING HERD IMMUNITY?

Infectious Diseases have been known to reach herd immunity, however, none have been permanently eradicated by it. For instance, although there was an observed decrease of measles infections during the 1930s, recent outbreaks indicate the disease is far from being eliminated – despite effective vaccination measures introduced in 1963.

 

IMPORTANT CONSIDERATIONS

As many countries enter into a second-wave of this pandemic, the bottom-line question for those who advocate the achievement of herd immunity through mass infection of the population will be one of cost-benefit. 

This prompts a few thoughts and questions. Any program to actively infect large numbers of individuals will begin with the isolation of the elderly and other high-risk populations. How many countries are truly equipped to house, feed, isolate, and treat millions of people in these categories? Do they have the manpower, physical structure, and funding?

It is important to note that the 2002-2004 SARS outbreak was not brought to an end by herd immunity, but rather through stringent public health methods implemented by affected countries. 

 

HOW MUCH TIME WILL BE REQUIRED TO ACHIEVE HERD IMMUNITY?

My country (Israel) has a population of 8.8 million and is currently experiencing 1,000 to 2,000 new cases per day. If we allow the current disease rate to continue, it will take perhaps three more years (!) to exceed 60 percent immunity. 

Would the Health System – already at capacity – be able to sustain all of this? Is there proof that COVID-19 infection even leads to immunity?  In what percentage of patients? Does immunity persist for more than a year or two?  Will immunity also “cover” newer strains of coronavirus?

Several COVID-19 vaccines will be released for general use in the next three to six months. Assuming that these vaccines are effective, targeted mass-infection at this point will cause more harm than good… and at best be a case of “too little, too late.”

 

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Antigen vs antibody – what is the difference?

Antigen vs antibody - 3D illustration
3D illustration of antigen in the human body

 

What is the difference between antigen vs antibody, and what role do they play in creating an effective vaccine? With the recent focus on the development of a COVID-19 vaccine there has been much talk of antigens and antibodies, often interchangeably, and little clarity on what they are – or the role they play in creating an effective vaccine. In this blog, we’ll cut through the jargon and discover the facts together.

Antigen

An antigen is any substance or organism that is unrecognized by our immune system. It could be anything from bacteria to chemicals, to viruses … or even foods [1]. Antigens typically trigger an immune response, which may consist of an antibody (more on that later), and are classified by their origins [2]:

  • Exogenous: entering from outside the body
  • Endogenous: generated from within
  • Autoantigens: proteins targeted in autoimmune diseases
  • Neoantigens (or tumor antigens): resulting from tumor cells.
  • Native antigens: An antigen which will later be processed by an antigen-presenting cell

In some cases, these main types have subtypes – but we won’t get into an immunology lecture today. An antigen-presenting cell is a cell that processes and then presents the antigen to T-cells (a form of white blood cells), which can then ‘handle’ the antigen, often by killing the offending cell [3].

Your immune system has “memory” which allows the system to deal with the offending antigen much more quickly and efficiently the next time it is encountered.  Vaccines are designed to simulate that first encounter with an antigen and create a robust memory in case the offending agent reappears in the future. [4].

The importance of vaccines is covered in more detail here, but in short, antigens themselves are crucial in the development of vaccines. Generally, the vaccine consists of a potentially hostile antigen, in a very weak or inactive form.

Antibody

Antibodies are proteins that bind with the antigen in order to neutralize the latter – or make other elements of the immune system “aware” of their presence.  Antibody-producing cells are specifically designed to tackle one type of antigen; and your blood, bone marrow, lymph glands, and spleen will contain millions of them to ensure that every known antigen will be confronted by a corresponding antibody  [5].

Antibodies are secreted by B leukocytes (a form of white blood cell) and circulate in blood plasma either freely or attached to the surface of a B cell.  The B and T cells work in unison to identify and locate antigens, create the correct antibodies, and capture (kill/neutralize) the antigen [6].

A vaccine, by exposing the immune system to a new antigen, will “teach” antibodies the correct format in which to capture or tag that antigen.  When the actual disease antigen later enters the body, the immune system will rapidly respond with minimal discomfort and inconvenience.

Effective vaccination needs both

To summarize – an antigen is a disease agent (virus, toxin, bacterium parasite, fungus, chemical, etc) that the body needs to remove, and an antibody is a protein that binds to the antigen to allow our immune system to identify and deal with it.

Woman with adhesive bandage on her shoulder
Antigens and antibodies work in tandem when vaccinating

 

Don’t take this all for granted, though. As impressive as our immune system is, it’s far from perfect and needs our assistance to prevent harmful antigens from entering the body – through hand washing, face masks, and social distancing. Look after your body and it will look after you!

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Want to learn more about vaccines? We’ve got a great ebook for you – GIDEON Guide to Vaccines and Globulin Preparations

References:

[1] M. Encyclopedia, “Antigen: MedlinePlus Medical Encyclopedia”, Medlineplus.gov, 2020. [Online]. Available: https://medlineplus.gov/ency/article/002224.htm

[2] “Antigens | Boundless Anatomy and Physiology”, Courses.lumenlearning.com. [Online]. Available: https://courses.lumenlearning.com/boundless-ap/chapter/antigens/. 

[3] T. Kambayashi and T. Laufer, “Atypical MHC class II-expressing antigen-presenting cells: can anything replace a dendritic cell?”, Nature Reviews Immunology, vol. 14, no. 11, pp. 719-730, 2014. Available: 10.1038/nri3754 

[4] A. Abbas, A. Lichtman and S. Pillai, Cellular and molecular immunology, 9th ed. Philadelphia: Elsevier, 2018, p. 97.

[5] C. Janeway, Immunobiology 5: the immune system in health and disease, 5th ed. Garland Publishing.

[6] L. Borghesi and C. Milcarek, “From B Cell to Plasma Cell: Regulation of V(D)J Recombination and Antibody Secretion”, Immunologic Research, vol. 36, no. 1-3, pp. 27-32, 2006. Available: 10.1385/ir:36:1:27

Varicella vs. Monkeypox

Outbreaks of varicella and monkeypox in Africa are occasionally mistaken for “smallpox”   The following table was generated by an interactive tool in Gideon (www.GideonOnline.com) which allows users to generate custom charts that contrast clinical features, drug spectra or microbial phenotypes.

 

 

 

Zika

When “Ebola” became a household word for most Americans in 2015, few realized that a more sinister outbreak was unfolding in their own back-yard. Chikungunya, a dengue-like illness which had previously been limited to the jungle areas of Africa and Asia, suddenly appeared in Latin America, resulting in over 2 million cases as of January 2016. And then Zika virus followed in the same region, threatening to attack a similar number of people. Unlike Chikungunya and Dengue, Zika virus infection has now been identified as a major cause of microcephaly (abnormally-small head) and other severe neurological disorders in babies born to women who are infected by Zika virus in early pregnancy.

GIDEON has been closely following Ebola, Chikungunya, Zika … and every other infectious disease – for over twenty five years. Health care profesionals can enter the signs and symptoms of patients from affected countries, and display a comprehensive, ranked list of possible diseases.

Findings of a recent patient treated after returning from Suriname with fever and rash were entered into GIDEON:

Suriname fever rash diagnosis

Note the red arrows to the right. GIDEON has indeed “considered” that the patient might be suffering from Chikungunya, Dengue, Zika – and a host of other common and lesser-known conditions.

Users can easily access extensive background information on the diseases themselves, including maps, pictures and graphs, or explore their status on the global level, or within individual countries.  In this example, GIDEON compares the clinical features of Dengue, Chikungunya and Zika:

Compare Chikunhunya Dengue Zika

GIDEON maps the current global distributions of these three diseases:

Zika Global Distribution Chikungunya Global Distribution Dengue Global Distribution

 

 

Diagnosis Support for Ebola through GIDEON

The Diagnosis module of Gideon is designed to generate a ranked differential diagnosis list for any Infectious Diseases scenario. In recent weeks, we’ve been running simulations of Ebola. The following link will access a Power Point “show” demonstrating one such scenario. Ebola case (Powerpoint)

Fun challenge using GIDEON to speculate about undiagnosed deaths in Zambia

Marjorie Pollack, an editor at ProMED, recently speculated about the cause of deaths in Zambia using GIDEON:

Speculation on a differential diagnosis with the symptoms given above — vomiting and backache — is a “fun” challenge. Checking the possible list of infectious agents that would produce the clinical spectrum of a cluster of severe, fatal infections associated with vomiting and backache in Zambia using the GIDEON (Global infectious disease and epidemiology network) database, comes up with a list of the following possible diagnoses (and probability of occurrence) — which includes viral, bacterial, and parasitic diseases:

Rift Valley fever (30.8 percent probability), leptospirosis (27.5 percent), influenza (2.4 percent), malaria (11.5 percent), meningitis — bacterial (9.2 percent), relapsing fever (3.2 percent), septicemia –bacterial (1.8 percent), legionellosis (1.4 percent). Other diseases mentioned with a less than one percent probability include: typhoid and enteric fever, _Bunyaviridae_ infections — misc., rabies, tuberculosis, typhus — endemic, _Streptococcus suis_ infection, yellow fever, trypanosomiasis — African, Q-fever, brucellosis, yersiniosis, ornithosis, trichinosis, infectious mononucleosis or EBV (Epstein-Barr virus) infection, poliomyelitis, toxoplasmosis.

Even more fun is the possible list of other diseases that might produce the same type of cluster, but anywhere in the world (not necessarily seen in Zambia at present). This list (according to the GIDEON network would include: hantavirus infections — Old World, Ebola, Lassa fever, typhus — scrub, dengue, hantavirus pulmonary syndrome, and Crimean-Congo hemorrhagic fever to mention a few.

GIDEON helped save a life with a correct differential diagnosis

In 2005 an agricultural expert from Israel went for 6 days to India to participate in a farming project. He returned to Israel, and the following morning developed fever, headache, vomiting and muscle pain.

Read the latest case of the month, Agriculture Expert in India, about how GIDEON helped save this person’s life.

ProMED uses GIDEON again

ProMED logoProMED provided another great example of how GIDEON can be used to diagnose an illness in Cote d’Ivoire:

When one checks GIDEON (Global Infectious Disease and Epidemiology Network) for the clinical picture associated with contact with animals, one gets 3 main possibilities — Q fever, ornithosis, and bunyaviridae. Of the bunyaviridae family, one does think of Rift Valley fever (RVF) as consistent with this clinical picture, but the involvement of poultry rules this out, as the RVF virus does not affect avians. Gideon also gives a “1st case scenario”, where it “ignores” the geographic location of the outbreak in the event that this is a new geographic extension of an otherwise known pathogen. In this case, the GIDEON program suggested Congo-Crimean hemorrhagic fever (CCHF).

GIDEON training videos – step by step instruction

Training videos for each of GIDEON’s features offer step by step tutorials and examples on how to maximize your use of GIDEON. The videos are flash based (like YouTube), so will work in any browser. All you have to do is turn up your speakers or put on your headphones and click the start button Play video button below the video.

Case of the month

We’ve received frequent request for one page examples of how to use GIDEON. “Case of the month” is an area of the website that demonstrates various aspects of GIDEON. Each case includes a PDF document that can be used as a handout.
For example, the case “West Nile Fever” – Staying in Real Time shows how to use GIDEON to keep track of the latest information regarding West Nile Fever globally.

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