- The Difference Between Vaccines and Antibody Therapeutics
- Vaccines vs. Antibody Biotherapeutics
- Passive Immunization
- Passive Immunity: Natural vs. Artificial
- The History of Passive Immunization
- Passive Immunization Today
- Advantages and Disadvantages of Passive Immunization
- Future Trends
- Vaccination and antibodies
- What's in a vaccine?
- What happens after vaccination?
- How does vaccination prevent disease?
- Different types of vaccines
- Are vaccines safe?
- The immune system and immunisation
- Lines of defence
- The immune response
- Antigens and antibodies
- Primary response
- Secondary response
- Types of immunisation
- How Vaccines Work
- The Herd Immunity Imperative
- Types of Vaccines
The Difference Between Vaccines and Antibody Therapeutics
Vaccines are considered to be among the greatest medical advances in the past several centuries. They have effectively eliminated some of the most deadly diseases ever to scourge humanity.
Study of the immune system has led to the development of antibody drugs, allowing medical researchers to harness the mechanisms that make vaccines so powerful in a specific, targeted manner.
In this way, the new class of drugs can take advantage of your body’s own ability to target and fight threats.
This picture from the Well Come Collection (wellcomecollection.org) is titled “Treatment of Infantile Paralysis” and depicts the results of Poliovirus. Fortunately, vaccines have virtually removed Poliovirus from our lives.
Vaccines work by utilizing your body’s immune system, which has the innate ability to respond to new threats. This is accomplished by introducing inactivated components of a disease to the body, giving it the chance to learn how to combat the disease without risk of infection.
When the real thing shows up, the immune system already has an antibody response prepared! Thanks to vaccines, some once-common diseases have been virtually eliminated. Polio is a crippling and sometimes deadly infectious disease that primarily occurs in children between six months and four years of age.
Infection may lead to permanent paralysis, or worse. The early 1950s saw many Poliovirus outbreaks throughout Europe, Australia, and the United States with more than 25,000 cases reported annually. This spurred the creation of the first effective polio vaccine in 1952.
New incidences dropped sharply over the following decades, and by 1994, vaccines had rendered the Americas effectively free of polio. Many other once-deadly diseases have been mostly eliminated in this way, including the measles, rubella, mumps, and smallpox.
Vaccines vs. Antibody Biotherapeutics
We have explained how antibody drugs work in previous blog posts. While they often take advantage of the abilities of your immune system, one of the biggest threats to their effectiveness is, ironically, the immune system itself.
Any protein-based drug has a risk of being perceived as “foreign” which will trigger an immune response to itself instead of to its target. This presents a serious hurdle with development.
The beauty of vaccines is that — un antibody drugs — they actively exploit your body’s immune response by giving it foreign material to “fight” which looks enough a real infection that your body learns what its enemy looks without ever facing a real threat.
In a sense, vaccines train your body to design and produce its own highly-specific antibody drugs against any new threat — without all the R&D!
Preparation of rabies vaccine from The Pasteur Institute, Kasauli, India. Photograph, ca. 1910.
Antibody drugs are powerful tools of modern medicine, capable of specifically binding and disabling all sorts of targets, but they are complicated and expensive to develop.
Vaccines let your body do the hard work and develop specialized antibodies to fight infections for itself.
In a sense, all the research done to create antibody drugs is just trying to replicate in a lab what the human body does on its own!
Links and Citations:
All pictures for this blog were provided by the Wellcome Collection: https://wellcomecollection.org/
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long term if they trigger a predominantly IgE response. This response could trigger an allergic reaction to future immunizations with the same antigens (IOM, 1994a).
To prevent the body's immune system from destroying its own tissues in what is known as an autoimmune response, immature T cells that react against self-antigens are thought to be destroyed in the thymus gland, creating what is known as central tolerance.
Peripheral tolerance might also occur, whereby those T cells that could potentially react to self-antigens and that are not destroyed in the thymus are somehow prevented from causing an autoimmune reaction.
Although studies suggest that peripheral tolerance exists, at least in experimental animals, the mechanism for the process is not yet known.
If peripheral tolerance exists in people, an autoimmune response might occur in response to vaccination if the vaccine somehow disrupts that peripheral tolerance or if peripheral tolerance is not strong on the day of vaccination (Miller et al., 1989).
Some people have suggested that vaccines can stimulate autoimmune reactions if some of the antigen fragments in vaccines resemble a person's self-antigens.
However, it is unclear why an immune system that is tolerant of its own self-antigens would respond to a self-antigen mimic in a vaccine.
Berkower speculated that vaccines might counter peripheral tolerance and foster an autoimmune reaction if they contain molecular mimics of self-antigens that are usually not exposed to T cells, because peripheral tolerance seems to depend on the continuous presence of an antigen.
Nakhasi suggested that an autoimmune response might be instigated by a vaccine or by natural infection if the microbial antigens bind to self-antigens in infected cells and change the antigens' shape such that they are no longer tolerated and can elicit an immune response.
According to McFarland, researchers suspect that molecular mimicry, which could possibly lead to an autoimmune disorder, might be occurring between self-antigens and antigens from microbes or vaccines if the two antigens share much of the same chemical structure.
Recent studies suggest, however, that they need to have a similar structure only in the narrow region that binds to the T-cell receptor (Vogt et al., 1994; Wucherpfennig et al., 1994).
In addition, the amino acids in this region do not have to be identical; rather studies suggest that they must have the same basic chemical and charge properties (Vogt et al., 1994; Wucherpfennig et al., 1994; Vergelli et al., 1996).
Some researchers have hypothesized that autoimmune diseases may be stimulated by viruses (Fujinami et al., 1985; Westall and Root-Bernstein, 1983). Westall and Root-Bernstein have postulated that this may occur if three criteria are met. The first one is that antigens are present that have molecular structure similar to self antigens found in certain human tissue (Westall and Root-
This article assumes familiarity with the terms antibody, antigen, immunity, and pathogen. See the Glossary for definitions.
A person may become immune to a specific disease in several ways. For some illnesses, such as measles and chickenpox, having the disease usually leads to lifelong immunity to it. Vaccination is another way to become immune to a disease.
Both ways of gaining immunity, either from having an illness or from vaccination, are examples of active immunity. Active immunity results when a person’s immune system works to produce antibodies and activate other immune cells to certain pathogens.
If the person encounters that pathogen again, long-lasting immune cells specific to it will already be primed to fight it.
A different type of immunity, called passive immunity, results when a person is given someone else’s antibodies. When these antibodies are introduced into the person’s body, the “loaned” antibodies help prevent or fight certain infectious diseases. The protection offered by passive immunization is short-lived, usually lasting only a few weeks or months. But it helps protect right away.
Passive Immunity: Natural vs. Artificial
Natural Infants benefit from passive immunity acquired when their mothers’ antibodies and pathogen-fighting white cells cross the placenta to reach the developing children, especially in the third trimester.
A substance called colostrum, which an infant receives during nursing sessions in the first days after birth and before the mother begins producing “true” breast milk, is rich in antibodies and provides protection for the infant. Breast milk, though not as rich in protective components as colostrum, also contains antibodies that pass to the nursing infant.
This protection provided by the mother, however, is short-lived. During the first few months of life, maternal antibody levels in the infant fall, and protection fades by about six months of age.
Artificial Passive immunity can be induced artificially when antibodies are given as a medication to a nonimmune individual. These antibodies may come from the pooled and purified blood products of immune people or from non-human immune animals, such as horses. In fact, the earliest antibody-containing preparations used against infectious diseases came from horses, sheep, and rabbits.
The History of Passive Immunization
Antibodies were first used to treat disease in the late 19th century as the field of bacteriology was emerging. The first success story involved diphtheria, a dangerous disease that obstructs the throat and airway of those who contract it.
In 1890, Shibasaburo Kitasato (1852-1931) and Emil von Behring (1854-1917) immunized guinea pigs against diphtheria with heat-treated blood products from animals that had recovered from the disease.
The preparations contained antibodies to the diphtheria toxin that protected the guinea pigs if they were exposed soon thereafter to lethal doses of diphtheria bacteria and its toxin. Next, the scientists showed that they could cure diphtheria in an animal by injecting it with the blood products of an immunized animal.
They soon moved to testing the approach on humans and were able to show that blood products from immunized animals could treat diphtheria in humans. The antibody-containing blood-derived substance was called diphtheria antitoxin, and public boards of health and commercial enterprises began producing and distributing it from 1895 onward.
Kitasato, von Behring, and other scientists then devoted their attention to treatment of tetanus, smallpox, and bubonic plague with antibody-containing blood products.
The use of antibodies to treat specific diseases led to attempts to develop immunizations against the diseases.
Joseph Stokes Jr, MD, and John Neefe, MD, conducted trials at the University of Pennsylvania under contract to the US Navy during World War II to investigate the use of antibody preparations to prevent infectious hepatitis (what we now call hepatitis A).
Their pioneering work, along with advances in the separation of the antibody-containing blood component, led to many studies on the effectiveness of antibody preparations for immunization against measles and infectious hepatitis.
Before the polio vaccine was licensed, health officials had hopes for the use of gamma globulin (an antibody-containing blood product) to prevent the disease. William M. Hammon, MD, of the University of Pittsburgh Graduate School of Public Health, building on Stokes’s and Neefe’s work, conducted important trials to test this idea in 1951-52.
He showed that administration of gamma globulin containing known poliovirus antibodies could prevent cases of paralytic polio. However, the limited availability of gamma globulin, and the short-term protection it offered, meant that the treatment could not be used on a wide scale.
The licensure of the inactivated Salk polio vaccine in 1955 made reliance on gamma globulin for poliovirus immunization unnecessary.
Passive Immunization Today
Today, patients may be treated with antibodies when they are ill with diphtheria or cytomegalovirus.
Or, antibody treatment may be used as a preventive measure after exposure to a pathogen to try to stop illness from developing (such as with respiratory syncytial virus [RSV], measles, tetanus, hepatitis A, hepatitis B, rabies, or chickenpox).
Antibody treatment may not be used for routine cases of these diseases, but it may be beneficial to high-risk individuals, such as people with immune system deficiencies.
Advantages and Disadvantages of Passive Immunization
Vaccines typically need time (weeks or months) to produce protective immunity in an individual and may require several doses over a certain period of time to achieve optimum protection.
Passive immunization, however, has an advantage in that it is quick acting, producing an immune response within hours or days, faster than a vaccine.
Additionally, passive immunization can override a deficient immune system, which is especially helpful in someone who does not respond to immunization.
Antibodies, however, have certain disadvantages. First, antibodies can be difficult and costly to produce.
Although new techniques can help produce antibodies in the laboratory, in most cases antibodies to infectious diseases must be harvested from the blood of hundreds or thousands of human donors.
Or, they must be obtained from the blood of immune animals (as with antibodies that neutralize snake venoms). In the case of antibodies harvested from animals, serious allergic reactions can develop in the recipient.
Another disadvantage is that many antibody treatments must be given via intravenous injection, which is a more time-consuming and potentially complicated procedure than the injection of a vaccine. Finally, the immunity conferred by passive immunization is short lived: it does not lead to the formation of long-lasting memory immune cells.
In certain cases, passive and active immunity may be used together. For example, a person bitten by a rabid animal might receive rabies antibodies (passive immunization to create an immediate response) and rabies vaccine (active immunity to elicit a long-lasting response to this slowly reproducing virus).
Monoclonal Antibodies Increasingly, technology is being used to generate monoclonal antibodies (MAbs)– “mono” meaning that they are a pure, single type of antibody targeted at a single site on a pathogen, and “clonal” because they are produced from a single parent cell. These antibodies have wide-ranging potential applications to infectious disease and other types of diseases.
Monoclonal antibodies were first created by researchers Cesar Milstein, PhD (1927-2002), and Georges Kohler, PhD (1946-1995), who combined short-lived antibody-producing mouse spleen cells (which had been exposed to a certain antigen) with long-lived mouse tumor cells. The combined cells produced antibodies to the targeted antigen. Milstein and Kohler won the Nobel Prize in Physiology or Medicine for their discovery in 1984.
To date, only one MAb treatment is commercially available for the prevention of an infectious disease.
This is a MAb preparation for the prevention of severe disease caused by RSV in high-risk infants.
Physicians are also increasingly using MAbs to combat noninfectious diseases, such as certain types of cancer, multiple sclerosis, rheumatoid arthritis, Crohn’s disease, and cardiovascular disease.
Scientists are researching other new technologies for producing antibodies in the laboratory, such as recombinant systems using yeast cells or viruses and systems combining human cells and mouse cells, or human DNA and mouse DNA.
Bioterror threats In the event of the deliberate release of an infectious biological agent, biosecurity experts have suggested that passive immunization could play a role in emergency response.
The advantage of using antibodies rather than vaccines to respond to a bioterror event is that antibodies provide immediate protection, whereas a protective response generated by a vaccine is not immediate and in some cases may depend on a booster dose given at a later date.
Candidates for this potential application of passive immunization include botulinum toxin, tularemia, anthrax, and plague. For most of these targets, only animal studies have been conducted, and so the use of passive immunization in potential bioterror events is still in experimental stages.
Antibodies were one of the first tools used against specific infectious diseases. As antibiotics came to be widely used, and as vaccines were developed, the use of passive immunization became less common.
Even today, however, antibodies play a role against infectious disease when physicians use antibodies to achieve passive immunity and to treat certain diseases in patients.
Scientists are investigating new applications for passive immunization and antibody treatment as well as new and more efficient methods of creating antibodies.
Vaccination and antibodies
Since the introduction of widespread vaccination programmes, millions of people have been protected against potentially fatal diseases, and countless lives have been saved.
Vaccines prepare your immune system to fight disease by taking advantage of the fact that the immune system can ‘remember’ infectious organisms. Vaccination gives us immunity without us having to experience the disease or its symptoms.
What's in a vaccine?
Each vaccine contains a killed or weakened form of the organism (usually a virus or bacterium) that causes a particular disease. Even though the organism in the vaccine has been altered so that it won’t make you ill, the part of the organism that stimulates your immune system to respond (the antigen) is still present.
While most vaccines work by inducing B lymphocytes to produce antibodies (see below), activation of T-cells — another type of immune system cell that helps protect against disease — is also important for some vaccines.
What happens after vaccination?
After you have been vaccinated, some of the cells that are responsible for protecting you against disease — your B lymphocytes — detect the antigens in the vaccine.
The B lymphocytes will react as if the real infectious organism was invading your body. They multiply to form an army of identical cells that are able to respond to the antigens in the vaccine.
The cloned cells then evolve into one of 2 types of cells:
- plasma cells; or
- memory B cells.
The plasma cells produce antibodies (Y- or T-shaped molecules), which are trained specifically to attach to and inactivate the organism you are being vaccinated against.
This response from your immune system, generated by the B lymphocytes, is known as the primary response. It takes several days to build to maximum intensity, and the antibody concentration in the blood peaks at about 14 days.
Your body continues making antibodies and memory B cells for a couple of weeks after vaccination. Over time, the antibodies will gradually disappear, but the memory B cells will remain dormant in your body for many years.
How does vaccination prevent disease?
The memory B cells (as the name implies) keep a memory of the organism that you were vaccinated against.
If you are ever exposed to that organism, the dormant memory cells will recognise it straight away, and rapidly start multiplying and developing into plasma cells.
Because the plasma cells have already been trained to produce antibodies against the organism, they are able to produce a large number of antibodies very quickly (within hours).
The antibodies attach to the invading organisms and prevent them from attacking your healthy cells. And because the antibodies are produced so quickly, they are able to fight the disease before you even get sick.
This accelerated and more intense immune response generated by the memory B cells is known as the secondary response. It is faster and more effective because all the preparations for the attack were made when you were vaccinated.
Different types of vaccines
Most vaccines are injected, but some can be given as a liquid that is swallowed. There are 4 main types of vaccines:
- live attenuated vaccines, which contain a living, but weakened, form of the germ (organism);
- inactivated vaccines, which contain a killed form of the organism;
- subunit vaccines, which contain just the part of the organism that stimulates an immune response (the antigen); and
- toxoid vaccines, which contain an inactivated bacterial toxin (toxoid).
While the live vaccines can provide lifelong immunity after only one or 2 doses, periodic booster doses are needed to maintain immunity with some of the other types of vaccines.
Are vaccines safe?
While vaccines can sometimes cause a mild reaction (such as soreness at the injection site or a slight fever), there are usually no serious adverse events associated with immunisation. Severe allergic reactions or serious side effects only very rarely occur.
Some people worry that the vaccine will cause the very disease that it is supposed to prevent. Occasionally, live attenuated vaccines cause a mild infection, but most people don’t get the disease or experience any symptoms. It is not possible for the other types of vaccines to cause disease in this way.
People with weakened immune systems and pregnant women should consult their doctor before having vaccinations.
For most people, not being immunised is a far greater risk to their health than any side effects associated with vaccination.
1. Immunise Australia Program. Frequently asked questions about immunisation (updated 28 Sep 2010). http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/faq (accessed Jul 2013).2. Australian Government Department of Health and Ageing. Australian Immunisation Handbook, 10th Edition 2013. 1.5 Fundamentals of immunisation. http://www.health.gov.
au/internet/immunise/publishing.nsf/Content/1-5 (accessed Jul 2013).3. Australian Government Department of Health and Ageing. Australian Immunisation Handbook, 10th Edition 2013. 2.2 Administration of vaccines. http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/handbook10-2-2 (accessed Jul 2013).4. Centers for Disease Control and Prevention (CDC).
How vaccines prevent disease (updated 25 Apr 2012). http://www.cdc.gov/vaccines/vac-gen/howvpd.htm (accessed Jul 2013).
5. Centers for Disease Control and Prevention (CDC). Principles of vaccination. In: Epidemiology and prevention of vaccine-preventable disease: Pink Book (12th Edition, May 2012). http://www.cdc.gov/vaccines/pubs/pinkbook/prinvac.
html (accessed Jul 2013).
The immune system and immunisation
The environment contains a wide variety of potentially harmful organisms (pathogens), such as bacteria, viruses, fungi, protozoa and multicellular parasites, which will cause disease if they enter the body and are allowed to multiply. The body protects itself through a various defence mechanisms to physically prevent pathogens from entering the body or to kill them if they do.
The immune system is an extremely important defence mechanism that can identify an invading organism and destroy it. Immunisation prevents disease by enabling the body to more rapidly respond to attack and enhancing the immune response to a particular organism.
Each pathogen has unique distinguishing components, known as antigens, which enable the immune system to differentiate between ‘self’ (the body) and ‘non-self’ (the foreign material).
The first time the immune system sees a new antigen, it needs to prepare to destroy it. During this time, the pathogen can multiply and cause disease.
However, if the same antigen is seen again, the immune system is poised to confine and destroy the organism rapidly. This is known as adaptive immunity.
Vaccines utilise this adaptive immunity and memory to expose the body to the antigen without causing disease, so that when then live pathogen infects the body, the response is rapid and the pathogen is prevented from causing disease.
Depending on the type of infectious organism, the response required to remove it varies.
For example, viruses hide within the body’s own cells in different tissues, such as the throat, the liver and the nervous system, and bacteria can multiply rapidly within infected tissues.
Lines of defence
The body prevents infection through a number of non-specific and specific mechanisms working on their own or together. The body’s first lines of defence are external barriers that prevent germs from entering.
The largest of all is the skin which acts as a strong, waterproof, physical barrier and very few organisms are able to penetrate undamaged skin. There are other physical barriers and a variety of chemical defences.
Examples of these non-specific defences are given below:
- Skin – a strong physical barrier, a waterproof wall
- Mucus – a sticky trap secreted by all the surfaces inside the body that are directly linked to the outside, also contains antibodies and enzymes
- Cilia – microscopic hairs in the airways that move to pass debris and mucus up away from the lungs
- Lysozyme – a chemical (enzyme) present in tears and mucus that damages bacteria
- Phagocytes – various cells that scavenge and engulf debris and invading organisms, which form part of the surveillance system to alert the immune system of attack
- Commensal bacteria – bacteria on skin and gut that compete with potentially harmful bacteria for space and nutrients
- Acid – in stomach and urine, make it hard for any germs to survive
- Fever – elevated body temperature making conditions unfavourable for pathogens to survive
The immune response
An immune response is triggered when the immune system is alerted that something foreign has entered the body. Triggers include the release of chemicals by damaged cells and inflammation, and changes in blood supply to an area of damage which attract white blood cells.
White blood cells destroy the infection or convey chemical messages to other parts of the immune system. As blood and tissue fluids circulate around the body, various components of the immune system are continually surveying for potential sources of attack or abnormal cells.
Antigens and antibodies
Antigens are usually either proteins or polysaccharides (long chains of sugar molecules that make up the cell wall of certain bacteria).
An antigen is a molecule that stimulates an immune response and to which antibodies bind – in fact, the name is derived from “antibody generators.” Any given organism contains several different antigens.
Viruses can contain as few as three antigens to more than 100 as for herpes and pox viruses; whereas protozoa, fungi and bacteria are larger, more complex organisms and contain hundreds to thousands of antigens.
An immune response initially involves the production of antibodies that can bind to a particular antigen and the activation of antigen-specific white blood cells.
Antibodies (immunoglobulins; Ig) are protein molecules that bind specifically to a particular part of an antigen, so called antigenic site or epitope. They are found in the blood and tissue fluids, including mucus secretions, saliva and breast milk.
There are five classes of antibody – IgG, IgA, IgM, IgD and IgE, which have a range of functions. They can act as ‘flags’ to direct the immune system to foreign material for destruction and form part of the innate / humoral immune response. Normally, low levels of antibodies circulate in the body tissue fluids.
However, when an immune response is activated greater quantities are produced to specifically target the foreign material.
Vaccination increases the levels of circulating antibodies against a certain antigen. Antibodies are produced by a type of white blood cell (lymphocyte) called B cells.
Each B cell can only produce antibodies against one specific epitope. When activated, a B cell will multiply to produce more clones able secrete that particular antibody.
The class of antibody produced is determined by other cells in the immune system, this is known as cell-mediated immunity.
Upon exposure to a pathogen, the body will attempt to isolate and destroy it. Chemicals released by inflammation increase blood flow and attract white blood cells to the area of infection.
Specialist cells, known as phagocytes, engulf the target and dismantle it. These phagocytes then travel to the nearest lymph nodes where they ‘present’ the antigens to other cells of the immune system to induce a larger, more specific response.
This response leads to the production of antigen-specific antibodies.
Circulating antibodies then find the organism and bind to its surface antigens. In this way it is labelled as the target. This specific response is also called the adaptive or cell-mediated immune response, since the immune system adapts to suit the type of invader.
When the body is first exposed to an antigen, several days pass before this adaptive response becomes active. Upon first exposure to a pathogen, immune activity increases, then levels off and falls. Since the first, or primary, immune response is slow it cannot prevent disease, although it may help in recovery.
Once antigen-specific T and B cells (lymphocytes) are activated, their numbers expand and following an infection some memory cells remain resulting in memory for the specific antigens. This memory can take a few months to fully develop.
During subsequent exposures to the same pathogen, the immune system is able to respond rapidly and activity reaches higher levels.
The secondary immune responses can usually prevent disease, because the pathogen is detected, attacked and destroyed before symptoms appear. In general, adults respond more rapidly to infection than children.
They are able to prevent disease or reduce the severity of the disease by mounting a rapid and strong immune response to antigens they have previously experienced.
In contrast, children have not experienced as many antigens and are more ly to get sick.
Memory of the infection is reinforced and long lived antibodies remain in circulation. Some infections, such as chickenpox, induce a life-long memory of infection. Other infections, such as influenza, vary from season to season to such an extent that even an adult is unable to adapt.
Vaccination utilises this secondary response by exposing the body to the antigens of a particular pathogen and activates the immune system without causing disease.
The initial response to a vaccine is similar to that of the primary response upon first exposure to a pathogen, slow and limited. Subsequent doses of the vaccine act to boost this response resulting in the production of long-lived antibodies and memory cells, as it would naturally following subsequent infections.
The aim of vaccines is to prime the body, so that when an individual is exposed to the disease-causing organism, their immune system is able to respond rapidly and at a high activity level, thereby destroying the pathogen before it causes disease and reduces the risk of spread to other people.
Vaccines vary in how they stimulate the immune system. Some provide a broader response than others.
Vaccines influence the immune response through the nature of the antigens they contain, including number and characteristics of the antigens, or through the route of administration, such as orally, intramuscular or subcutaneous injection.
The use of adjuvants in vaccines can help to determine the type, duration and intensity of the primary response and the characteristics of resulting antigen-specific memory.
For most vaccines, more than one dose may be required to provide sustained, long-lasting protection – to be fully immunised.
Types of immunisation
Active immunisation – body generates its own response to protect against infection through specialised cells and antibodies, as stimulated by vaccines. Full protection takes time to develop but is long lasting.
Passive immunisation – ready-made antibodies are passed directly to the person being immunised. This allows for immediate protection, but passive immunisation may only last a few weeks or months.
Antibodies are passed from mothers to infants across the placenta and in breast milk, to protect the infants for a short time after birth.
Antibodies (immunoglobulins) are also purified from blood or in laboratories; these can be directly injected to provide rapid but short lived protection or treatment for certain diseases, such as rabies, diphtheria and tetanus.
How Vaccines Work
A vaccine works by training the immune system to recognize and combat pathogens, either viruses or bacteria. To do this, certain molecules from the pathogen must be introduced into the body to trigger an immune response.
These molecules are called antigens, and they are present on all viruses and bacteria.
By injecting these antigens into the body, the immune system can safely learn to recognize them as hostile invaders, produce antibodies, and remember them for the future.
If the bacteria or virus reappears, the immune system will recognize the antigens immediately and attack aggressively well before the pathogen can spread and cause sickness.
The Herd Immunity Imperative
Vaccines don't just work on an individual level, they protect entire populations. Once enough people are immunized, opportunities for an outbreak of disease become so low even people who aren't immunized benefit.
Essentially, a bacteria or virus simply won't have enough eligible hosts to establish a foothold and will eventually die out entirely.
This phenomenon is called “herd immunity” or “community immunity,” and it has allowed once-devastating diseases to be eliminated entirely, without needing to vaccinate every individual.
This is critical because there will always be a percentage of the population that cannot be vaccinated, including infants, young children, the elderly, people with severe allergies, pregnant women, or people with compromised immune systems. Thanks to herd immunity, these people are kept safe because diseases are never given a chance to spread through a population.
Public health officials and scientists continue to study herd immunity and identify key thresholds, but one telling example is the country of Gambia, where a vaccination rate of just 70% of the population was enough to eliminate Hib disease entirely.
However, if too many people forgo vaccinations, herd immunity can break down, opening up the population to the risk of outbreaks. That is why many officials and doctors consider widespread immunization a public health imperative and blame recent disease outbreaks on a lack of vaccination.
For example, in 1997, prominent medical journal The Lancet published research claiming to have found a link between the measles vaccine and autism. As a result, in following years the parents of over a million British children decided not to vaccinate their kids.
The research has since been thoroughly debunked, but the number of measles cases has skyrocketed, from just several dozen a year in 1997 to over 2,000 cases in 2011.
Similar outbreaks have occurred throughout the United States, involving both measles and whooping cough, with doctors and officials blaming low rates of vaccination.
Types of Vaccines
The key to vaccines is injecting the antigens into the body without causing the person to get sick at the same time. Scientists have developed several ways of doing this, and each approach makes for a different type of vaccine.
Live Attenuated Vaccines: For these types of vaccines, a weaker, asymptomatic form of the virus or bacteria is introduced into the body. Because it is weakened, the pathogen will not spread and cause sickness, but the immune system will still learn to recognize its antigens and know to fight in the future.
- Advantages: Because these vaccines introduce actual live pathogens into the body, it is an excellent simulation for the immune system. So live attenuated vaccines can result in lifelong immunity with just one or two doses.
- Disadvantages: Because they contain living pathogens, live attenuated vaccines are not given to people with weakened immune systems, such as people undergoing chemotherapy or HIV treatment, as there is a risk the pathogen could get stronger and cause sickness. Additionally, these vaccines must be refrigerated at all times so the weakened pathogen doesn't die.
- Specific Vaccines:
- Rubella (MMR combined vaccine)
- Varicella (chickenpox)
- Influenza (nasal spray)
Inactivated Vaccines: For these vaccines, the specific virus or bacteria is killed with heat or chemicals, and its dead cells are introduced into the body. Even though the pathogen is dead, the immune system can still learn from its antigens how to fight live versions of it in the future.
- Advantages: These vaccines can be freeze dried and easily stored because there is no risk of killing the pathogen as there is with live attenuated vaccines. They are also safer, without the risk of the virus or bacteria mutating back into its disease-causing form.
- Disadvantages: Because the virus or bacteria is dead, it's not as accurate a simulation of the real thing as a live attenuated virus. Therefore, it often takes several doses and “booster shots” to train the body to defend itself.
- Specific Vaccines:
- Polio (IPV)
- Hepatitis A
Subunit/conjugate Vaccines: For some diseases, scientists are able to isolate a specific protein or carbohydrate from the pathogen that, when injected into the body, can train the immune system to react without provoking sickness.
- Advantages: With these vaccines, the chance of an adverse reaction in the patient is much lower, because only a part or the original pathogen is injected into the body instead of the whole thing.
- Disadvantages: Identifying the best antigens in the pathogen for training the immune system and then separating them is not always possible. Only certain vaccines can be produced in this way.
- Specific Vaccines:
- Hepatitis B
- Haemophilus Influenzae Type B (Hib)
- Pertussis (part of DTaP combined immunization)
- Human Papillomavirus (HPV)
Toxoid Vaccines: Some bacterial diseases damage the body by secreting harmful chemicals or toxins.
For these bacteria, scientists are able to “deactivate” some of the toxins using a mixture of formaldehyde and water. These dead toxins are then safely injected into the body.
The immune system learns well enough from the dead toxins to fight off living toxins, should they ever make an appearance.
- Specific Vaccines:
Conjugate Vaccines: Some bacteria, those of Hib disease, possess an outer coating of sugar molecules that camouflage their antigens and fool young immune systems.
To get around this problem, scientists can link an antigen from another recognizable pathogen to the sugary coating of the camouflaged bacteria.
As a result, the body's immune system learns to recognize the sugary camouflage itself as harmful and immediately attacks it and its carrier if it enters the body.
- Specific Vaccines:
- Haemophilus Influenzae Type B (Hib)
DNA Vaccines: Still in experimental stages, DNA vaccines would dispense with all unnecessary parts of a bacterium or virus and instead contain just an injection of a few parts of the pathogen's DNA.
These DNA strands would instruct the immune system to produce antigens for combating the pathogen all by itself. As a result, these vaccines would be very efficient immune system trainers.
They are also cheap and easy to produce.
- Specific Vaccines: DNA vaccines for influenza and herpes are currently in human testing phases.
Recombinant Vector Vaccines: These experimental vaccines are similar to DNA vaccines in that they introduce DNA from a harmful pathogen into the body, triggering the immune system to produce antigens and train itself to identify and combat the disease.
The difference is that these vaccines use an attenuated, or weakened, virus or bacterium as a ride, or vector, for the DNA.
In essence, scientists are able to take a harmless pathogen, dress it in the DNA of a more dangerous disease, and train the body to recognize and fight both effectively.
- Specific Vaccines: Recombinant vector vaccines for HIV, rabies, and measles are currently being developed.
Last Updated: November 22, 2019