Infectious Disease: The effectiveness of immunisation programs
Infectious diseases have been some of the leading causes of death for centuries and up until the introduction of the vaccine in 1796 there were no preventative measures. Vaccines allow for preventative action which is vital in the cases of diseases which either have no, low or easily missed symptoms or in such cases where exposure to the disease is often fatal especially in the case of Smallpox, Polio and Diphtheria. Immunisation programs are largely effective and in some cases, such as smallpox, can lead to the complete eradication of the virus, whilst in most cases, such as diphtheria, will greatly reduce the spread and occurrence of the disease.
Introduction to the Immune Response:
In order to understand the working of vaccinations and its impact on the immune response, it is important to first understand the way the immune response works. The immune response is composed of three main parts, that is T cells, B cells and Antibodies. T cells and B cells are both lymphocytes (a form of white blood cells) that act against specific antigens, this means that each lymphocyte only acts against a specific foreign antigen. There are two types of B cells: Plasma B cells and Memory B cells and there are four types of T cells: Helper T cells, Cytotoxic T cells, Memory T cells and Suppressor T cells. Helper T cells have a surface receptor protein which allows them to recognise a foreign antigen. When a Helper T cell recognises the antigen as the one that matches their surface receptor protein they become activated. Helper T cells then release a chemical which activates both the Cytotoxic T cells and the Plasma B cells. Cytotoxic T cells are those that kill the invading foreign body. Cytotoxic T cells can clone themselves so as to bind with the infected cells. Plasma B cells produce antibodies that are specific to the particular antigen. These Antibodies move to the site of infection and combine with the antigen forming an antigen-antibody complex, thus deactivating it. Once the foreign antigen is destroyed, Suppressor T cells terminate the activity of the Plasma B cells and Cytotoxic T cells. Both the Cytotoxic T cells and Plasma B cells are vital as the T cells are responsible for cell-mediated immunity whilst the B cells are responsible for antibody-mediated immunity. This process (primary response) is quite a lengthy process and it means that the organism fighting the infection has to have the infection in their system for a considerable length of time. To reduce this, should the organism contract the infection again (secondary response), there are memory T cells and Memory B cells who are responsible for ensuring that the organism responds more rapidly to future invasions by the same antigen thus ensuring that the required antibody will then be produced more quickly, and in larger amounts, allowing for a more efficient immune response.
Vaccinations in relation to the immune response:
Vaccinations work by essentially bypassing the primary response. Instead of a naturally acquired immunity is an artificially acquired immunity. Vaccinations introduce a weakened strain of the antigen so that it is not powerful enough to harm the body, however, it still contains enough of the antigens to allow the body to trigger an immune response thus building up immunity and meaning that if they body, were it to encounter this virus again in a natural setting, the body would respond with a secondary response because the vaccination has built up a level an initial level of immunity. This is called an Active Artificial Immunity (See fig. 1).
Another way vaccinations can work is through Passive Artificial Immunity (See fig. 1) when antibodies, as opposed to antigens, are introduced to the organism, resulting in short term immunity. The immunity is short term as no memory cells have been produced. Passive Artificial Immunity is used, mostly, in the cases of very young children or the weak or elderly who could be negatively impacted by the strain used in Active Artificial Immunity because of the persons weakened state.
These are both examples of personal immunity, meaning that those who have been vaccinated develop an immunity to a specific disease they were inoculated against. There is, however, another way in which vaccinations can help create immunity: herd immunity. Herd Immunity relies on the majority of the population being immunised, it works on the principle that susceptible individuals are needed to spread the disease. If the majority of the population is immunised against a disease, they can’t contract the disease therefore it is less likely to spread as it doesn’t have any human carriers. Herd Immunity is important in protecting members of the community who cannot be vaccinated, for example very young children, cancer patients and people with immune system problems.
Vaccinations are a highly successful mechanism of protecting individuals and the community against disease. The first vaccination developed was for Smallpox (Variola) and was developed in 1796 by Edward Jenner who, after noticing that the dairymaids who contracted cowpox did not contract smallpox, infected his gardeners son with pus from a cowpox (vaccinia) blister. The child was immune from smallpox because Vaccinia (cowpox) and Variolea (smallpox) are very closely linked and by inoculating his gardeners son with the cowpox disease it gave him immunity to Smallpox. Smallpox is a highly infectious disease which is spread via airborne particles or through human contact. Major symptoms include blistering on the skin, fever and headaches among other symptoms. There are two strains of smallpox: Variola Major (which if contracted is usually fatal) and Variola Minor (rarely fatal).
Occurrence and Spread of Smallpox Prior to Vaccination:
The origins of smallpox are unknown, however, it can be dated back to at least the 3rd century BC. It spread throughout the centuries, in the 6th century it was introduced into Japan via trade, in the 7th century Arabic expansion brought it to northern Africa, Spain, and Portugal, in the 11th century crusaders further spread smallpox in Europe, in the 15th century Portuguese exploration introduced it to Western Africa, in the 16th century European colonisation and the African slave trade spread smallpox throughout the Caribbean, in the 17th century European colonisation introduced smallpox into North America and in the 18th century English settlers introduced smallpox into Australia. Due to Australia’s isolation, however, the last case was in 1938, long before it was eradicated in other parts of the globe.
Occurrence and Spread of Smallpox After Vaccination:
Smallpox was one of the big killers and had a high mortality rate: it killed some 400,000 people in Europe each year during the 18th century, was responsible for 1/10 of all deaths in Europe in the 19th century and killed more than 300 million people in the 20th century. Eradicating the disease was a high priority for some of the major health organisations such as The World Health Organisation (WHO) and The Pan American Health Organisation (PAHO) who established mass immunisation programs in an effort to eradicate the disease. Despite the vaccine being developed back in the late 1700s it was not commonplace until the 1800s. The Smallpox vaccination was made free in the 1940s and soon after became a compulsory vaccination. In the 1950s the PAHO used an immunisation program to eradicate smallpox and was successful, eliminating smallpox from almost all American countries excluding some South American countries.
In 1959 the WHO initiated the “Global Smallpox Eradication Program”, however, it lacked the funds and support to make any radical change. In 1967 the WHO begun the Intensified Eradication Program, implementing a worldwide immunisation program aiming to eradicate the disease entirely. By the time the Intensified Eradication Program was implemented smallpox had already been successfully eliminated in Australia (1938), North America (1952) and Europe (1953). Prior to the implementation of the WHO program there were 10-15 million cases of smallpox, resulting in 2 million deaths annually. It was an exceedingly effective program, however, and the last case of smallpox was in Somalia in 1977 and the disease was declared eradicated in 1980.
Evaluation of the Success of the Smallpox Vaccine:
It has killed more people than any other infectious disease and the eradication of the disease saves approximately 5 million lives every single year. Thanks to a successful vaccination program the Smallpox vaccine made history as the first, and currently only, vaccine to completely eradicate any disease. It was an extremely successful vaccination and by using strategies such as: mass immunisation programs with supplementary doses given on specific “immunisation days”; surveying the occurrence of new cases of smallpox; ring vaccination (See fig. 2); and herd immunity helped to eradicate the disease completely. The only remaining strains of the Variola virus are in research labs. The only concerns regarding smallpox in this day and age is the continued threat of bioterrorism, in which the Variola virus could be reintroduced outside a laboratory environment in an act of bioterrorism.
Although all vaccinations do not always completely eradicate the disease, as in Smallpox, they can greatly reduce the risks associated with it. Diphtheria (Diphtheriae) is a highly contagious bacterial infection which attacks the lining of the respiratory system and causes breathing difficulties. There are three main strains of diphtheria: Corynebacterium diphtheriae, Corynebacterium ulcerans and, albeit rarely, Corynebacterium pseudotuberculosis. These strains can cause one of four types of diphtheria: respiratory diphtheria, laryngeal diphtheria, nasal diphtheria and cutaneous diphtheria. Diphtheria forms a thick pseudomembrane around the nose and throat and can cause nerve damage, heart failure and in extreme cases it can be fatal. Major symptoms include weakness, sore throat, fever and swollen neck glands among others. This is a particularly dangerous set of symptoms as they are rather close to the common cold so many people do not automatically recognise them, this is why it is particularly important to receive the vaccination as a preventative measure because the symptoms usually go unnoticed initially. Diphtheria is mainly spread via airborne particles, secretions from the nose and throat and infected skin wounds. Earlier stages of research into diphtheria were undertaken by L. Brieger, C. Fraenkel, F. Wernicke and T. Smith and the first successful vaccine for Diphtheria was developed in 1913 by Emil von Behring using a toxin-antitoxin mixture not only as a vaccine but also as a cure for those who have contracted the disease.
Occurrence and Spread of Diphtheria Prior to Vaccination:
The origin of the disease is unknown, however, it is first mentioned by Hippocrates in the 5th century BC. Prior to the vaccine, case-fatality rates were high, reaching 50% in some areas during the major diphtheria epidemic in Europe and the US in the 1880s. In 1912, the year prior to the invention of the vaccine approximately 11,000 people in America died from Diphtheria and Croup making it the 9th highest cause of death that year.
Occurrence and Spread of Diphtheria After Vaccination:
In 1921, the US had 206 000 cases reported with 15,500 deaths, this encouraged the introduction of immunisation programs against diphtheria. Immunisation programs were introduced in Australia between 1930-1940, which resulted in the rapid decline of diphtheria in Australia, indeed there has been only one reported case in Australia between 1994-2006. The WHO introduced the EPI (Extended Program Immunisation) in 1974. Prior to the program only 5% of children globally were immunised against diphtheria. This is not to say that because of the immunisation program it stopped immediately. In the 1980s, there were around 1 million cases and 50,000-60,000 deaths due to diphtheria every year in developing countries. By the 1990s, however, due to the continued success of the immunisation program, the rate of immunisation against diphtheria rose from 5%, prior to the 1970s, to 80%. This impressive rise in immunisation paralleled the drop in the mortality rate globally (see fig. 3). By the 2000s the disease had dropped by 90% from its occurrence and case-fatality rates in 1980.
Evaluation of the Success of the Diphtheria Vaccine:
There is still a concern about Diphtheria because, even though there has been a significant reduction in rates of Diphtheria, it still occurs, especially in developing countries which have a relatively poorer EPI coverage. Overall the immunisation program for Diphtheria has proven especially effective, however, immunisation programs need to continue, with a special focus on developing countries, in the hopes that it may be as successful as the Smallpox vaccination.
Vaccinations programs can be highly effective, such as, with the smallpox vaccination and extended vaccination programs, such as with the Diphtheria EPI which significantly reduced both the occurrence and the case-fatality rates. Polio (Poliomyelitis) is a viral disease that causes paralysis which can be fatal. The first successful and approved polio vaccine was developed in 1955 by Jonas Salk. Devastatingly, whilst the vaccine was in its trial period it infected some 200 children, many of whom died. Salk’s was the first vaccine developed for polio, however, in 1960 Albert Sabin introduced an oral vaccine which replaced Salk’s due to it being cheaper, easier to use and containing a live weakened strain as opposed to a dead one. Neither of these doctors patented their vaccines, instead, presenting them as their contribution to making the world a better, safer place.
There was, and is, no known cure to the disease so the development of the vaccines were vital. It is particularly difficult to recognise polio as over 90% of infections cause no symptoms unless it has entered the blood stream, if it has, then symptoms include: fever; headaches; speech, swallowing and breathing difficulties and paralysis.
Occurrence and Spread of Polio Prior to Vaccination:
These vaccines were vital as in the early 1950s, prior to the release of either vaccine 25,000 to 50,000 new cases of polio occurred each year, mainly affecting children under the age of five. In Australia alone, there were over 590,000 cases between the 1930s and the 1950s of which 800 proved fatal. Indeed it was so prevalent that summer was referred to as “polio season” due to the high occurrence of polio infections in the summer. Polio is spread via person to person contact, and enters through the mouth and then spreads into the environment through faecal matter.
Occurrence and Spread of Polio After Vaccination:
In 1988 the WHO introduced the Global Polio Eradication Initiative which aims to eradicate polio. The eradication plans focus on preventative measures with a focus on immunising children and in 1997 the Global Polio Eradication Initiative immunised 450 million children. The main strains of the polio virus are Wild Poliovirus type 1, Wild Poliovirus type 2 and Circulating Vaccine-Derived Poliovirus. This second strain, Circulating Vaccine-Derived Poliovirus, have the opposite effect of herd immunity, if a population is under immunised then Circulating Vaccine-Derived Poliovirus can mutate into a form which may adversely affect the population. Currently polio remains endemic in 3 countries, Afghanistan, Nigeria and Pakistan. Overall, however, the polio vaccination has resulted in a reduction of almost 60-70% of polio cases.
Evaluation of the Success of the Polio Vaccine:
The Global Polio Eradication Initiative aimed to have polio completely eradicated by 2010, however, was unsuccessful and established the Eradication and Endgame Strategic Plan which is effective between 2013 and 2018. Although it does not appear that Polio will be eradicated by the end of the programme significant progress through their use of the immunisation programs has been achieved.
Overall the vitality of immunisation programs can be seen in the three examples listed above. Because of the effectiveness of the smallpox immunisation program and the global efforts provided by the WHO smallpox has been successfully eradicated and is no longer a concern for the general population. The Diphtheria Vaccination Program is following in the footsteps of the Smallpox Program significantly reducing the Diphtheria rate. Polio still has a long way to go in terms of reduction of cases, however, it has undeniably reduced the occurance of Polio globally. Because of the need for consistent immunisations programs in all countries, Australia has recently stepped up deducting $28 fortnightly for every unvaccinated child from the tax benefits given to many families. This is in order to encourage the vaccination of children because children are especially at risk. Third world countries continue to be an area in which vaccinations need to be more thoroughly implemented and reports such as the Global Polio Eradication Initiative Midyear Report show the way in which some factors like superstition, anti-vaccination and gender disparity play into the lack of vaccinations given. Overall extensive programs such as the Intensified Eradication Program, the Extended Program Immunisation and the Global Polio Eradication Initiative have helped to greatly reduce, or in the case of smallpox, completely eradicate, infectious diseases which were once considered some of the biggest killers on the planet.