Vaccines 101: A brief introduction

Vaccination has been referred to as one of the greatest advances in medical history. However, recently controversy regarding vaccine safety has been uttered. In our first article breaking down science we will introduce you to vaccines, following up with a series of articles digging deeper into the science.

Brief history

The history of vaccines can be tracked much further back than modern medicine [1]. An observation by Thucydides in 430 BC Athens described how people surviving smallpox infection did not get infected again. Starting in tenth century China, healthy people were exposed to infected tissue in a form of vaccination known as variolation. In the eighteenth century variolation arrived in England, and although it occasionally led to death, it caused milder illness and smallpox rates were a lot lower in populations who made use of this method. In 1796 vaccination as we know them were developed by Dr Edward Jenner. Although the popularity of vaccines increased in the 19th century a violent opposition formed in the 1870s. Following the vaccine against rabies in the 1880s, many more vaccines were quickly developed, and vaccines for diphtheria, tetanus, whooping cough and tuberculosis were developed by the late 1920s. Although many vaccines have been developed, the vaccine against the smallpox has bar far been the most remarkable achievement. With WHO’s global effort starting in 1958 the vaccine was responsible for the first and currently only eradication of a human disease in 1980 [2].


So how do vaccines work?

Vaccines can be divided into two main groups: live attenuated vaccines and inactivated vaccines [3]. The first group uses a weakened form of the bacteria or virus, whereas the latter uses the killed forms or products of the bacteria or viruses in question. Live attenuated vaccines are the most effective type as they can induce life-long immunity. The full mechanism and interactions of the disease is retained in these vaccines, which will lead to much more effective immunity than conferred by inactivated vaccines. Inactivated vaccines can be further divided into multiple groups: whole killed vaccines, subunit vaccines, toxoid vaccines, and conjugate vaccines [4]. Subunit vaccines are comprised of some of the antigens expressed by the bacteria or virus. These antigens are what the antibodies of our immune cells bind to and subsequently start a cascade of events leading to further production of cells with these antibodies. Some vaccines contain toxoids which are inactivated forms of the toxins that some bacteria release. The immune system’s response to toxins are the same as to those of antigens. Conjugate vaccines consist of pathogen specific polysaccharides that are attached to a product known to induce a strong immune response. These ingredients of a vaccine are referred to as the active ingredients.

In addition to the active ingredients, vaccines contain other excipients. The excipients are there to prolong the shelf-life and improve the efficiency of vaccines. Adjuvants increase the immune response of the body to the vaccine, preservatives help to avoid contamination of the vaccines, and stabilizers keep the vaccines potent [3]. Some of the licensed adjuvants and stabilizers used in the UK and US along with what vaccines they are used in can be seen in the tables. Some of these ingredients have been a cause for concern for many people. Some people may be allergic to some of the stabilizers used in vaccines, such as sorbitol, sucrose, lactose, egg protein, yeast protein and latex. In some cases, different make-ups exist for the same type of vaccine, and one can thus avoid the allergens by getting an alternative injection. Other times the allergen is only present in trace amounts and clinical testing have shown no allergic reaction. No matter the case, it is recommended that allergies are mentioned to your doctor prior to receiving a vaccination. The ingredient human serum albumin, although screened and processed for contaminations, will be phased out in the UK during this year [5].


What about autism?

To some, the presence of specific compounds such as thimerosal (a preservative based on ethyl-mercury) has caused upset. Due to the common understanding of the dangers of mercury it for obvious reasons causes worry when injecting people with that it. However, the form of mercury that is highly toxic is methyl-mercury, which is not used in vaccines, whereas the ethyl-mercury used in vaccines is very quickly removed from the body [6]. With that said, thimerosal was removed from UK vaccines between 2003 and 2005 and are only present in some non-routine vaccines [7]. According to the FDA all routine vaccines in the US for children under the age of 6 and below exist in non-thimerosal forms [8]. Furthermore, of the 18 seasonal flu vaccines, only 5 of them contain thimerosal and one of them contain trace amounts [8].

Despite the removal of thimerosal from vaccines, autism rates have continued to increase, which does not support the hypothesis that thimerosal causes autism. This along with other evidence has led the CDC to conclude no link between thimerosal and autism [9], and the UK-based National Autistic Society to more specifically state no link between autism and the MMR vaccine [10]. Due to space constraints I shall refrain from reviewing this science in this article. We will follow up with an article that does so but will in the mean time encourage you to review the science for yourselves. With that in mind let us have a look at some of the side effects that have been established.

On the table to the right, you can read the “severe adverse effects” of the MMR and DTwP vaccines. WHO’s reports on these vaccines along with others can be found on their website. These vaccines are part of routine vaccination programs for children in many countries. What’s important to note is whether the side effects actually lead to long-term health complications. For example, in the instance of the MMR vaccine, WHO noted that the seizure caused by the measles component are not linked to the development of neurological disorders, nor is HHE episodes of the DTwP vaccine associated with neurological damage. Further, certain risk groups can be defined that are more prone to certain side effects than other individuals. E.g. seizures after vaccination has been reported in 27 % of patients with Dravet’s syndrome, but only 0,008 % overall.


Is it worth the side effects?

That’s not a simple question to answer. Not only do side effects occur at different rates, but some are worse than others. And the severity also depends on what predisposition the individuals in question have. So, when it comes to it it’s almost an impossible question to answer. Let us however try, using measles as an example.

WHO describes measles as one of the world’s most contagious diseases [11]. The area or surface that the virus has infected may remain contagious for up to two hours, and the transmission from person to person can occur 4 days before symptoms appear. Although we have a vaccination for the disease, no specific antiviral treatments exist. According to the Vaccine Knowledge Project, the mortality rate of measles infections in high income regions of the world is 1 in 5000 [12]. Vaccination has decreased the rate of deaths caused by measles globally over the past two decades, with 872,000 deaths in 1990 and only 110,000 in 2017 [12]. In 2017, 277 cases of measles were confirmed in England and Wales [13], in contrast to the 460,407 cases notified of in 1967 (the year before the introduction of the vaccine) [14]. The population of England and Wales in 1971 (oldest data available) was 49,152,000 and in 2017 it was 58,744,600 [15,16]. A little math (assuming the population size in 1967 was as high as 1971) will tell you that the difference between the occurrence of the disease has gone from approximately 9367 in a million to 4.7 in a million. Pre-dating the vaccine, you had a greater chance of catching the disease than you have of experiencing a side effect of the vaccine. The chance of being infected and subsequently dying of measles was 1967 was 2 in a million. If we account for the medical advances since then and use today’s mortality rate of measles to calculate the probability, it would only be reduced to 1.9 in a million. In 2017, the theoretical chance of contracting measles and dying was 0.00094 in a million (I was not able to find any data on the number of deaths caused my measles in the UK in that year). Bearing in mind the symptoms that the disease leads to and the chance of being infected before the vaccine, the side effects might not seem like a bad trade. Let alone the chance of dying. This way of looking at it is obviously very simplified but I hope it shines some light on the difference vaccines make. Thinking about the difference in deaths before and after the introduction of the vaccine and the side effects of it, I will let you make up your own mind about it. Do share your thoughts in the comments section either her or on Facebook.


Herd immunity

As the last thing let us briefly mention herd immunity before I let you carry on with your day, for which the science behind we shall touch upon in an upcoming article. Simply put when a high proportion of a community is immune to a disease [17], the community as a whole will become immune. However, if only a very few number of individuals are immune, herd immunity will not take place. This is due to the chance of the primary host of the disease meeting another possible host being lowered as the amount of immune people is increased. Think of immune people as a physical barrier. However, as the number is decreased the disease will no longer be contained and everyone who is not immune will quickly be infected. This means that vaccinating as many people as possible will help protect the proportion of a population that remains unvaccinated. The unvaccinated proportion may be groups of people with conditions that will lead to severe complications if vaccines are administered, or where immunity is not conferred to the same extent. E.g. people with immunodeficient disorders, who by the well nature of vaccines will have complications. If individuals with such disorders get infected with the actual disease their chance of survival is decreased compared to others, and thus herd immunity plays an important role. If enough people are vaccinated, they will be protected even if they have not received the vaccine themselves. Vaccination suddenly becomes more than just the problem of an individual, but a society wide effort.



[1] National Health Service (2016). The history of vaccinations.
[2] 33rd World Health Assembly (1980). Declaration of global eradication of smallpox.
[3] Pulendran & Ahmed (2011). Immunological mechanisms of vaccinations.
[4] Oxford vaccine group, University of Oxford (2019). Types of Vaccines.
[5] National Health Service (2019). Vaccine ingredients.
[6] World Health Organization (2006). Statement on thiomersal.
[7] Oxford vaccine group, University of Oxford (2019). Vaccine ingredients.
[8] U.S. Food and Drug Administration (2018). Thimerosal and Vaccines.
[9] Centers for Disease Control and Prevention (2015). Thimerosal in Vaccines.
[10] National Autistic Society. Our position – MMR vaccine.
[11] World Health Organization (2018). Measles.
[12] Oxford vaccine group, University of Oxford (2019). Measles.
[13] Public Health England (2018). Confirmed cases of measles, mumps and rubella in England and Wales: 1996 to 2017.
[14] Public Health England (2017). Measles notification and deaths in England and Wales: 1940 to 2016.
[15] Office for National Statistics (2018). England population mid-year estimate.
[16] Office for National Statistics (2018). Wale population mid-year estimate.
[17] Anderson & May (1985). Vaccination and herd immunity to infectious diseases.
[18] U.S. Food and Drug Administration (2018). Common Ingredients in U.S. Licensed Vaccines.
[19] National Health Service (2016). Childhood vaccines timeline.
[20] DataPharm Communications Ltd. Electronic Medicines Compendium (eMC).
[21] Centers for Disease Control and Prevention (2018). Vaccine Excipients & Media Summary.
[22] World Health Organization (2014). Observed rate of vaccine reactions – Measles, mumps and rubella vaccines.
[23] World Health Organization (2014). Observed rate of vaccine reaction – Diphtheria, pertussis, tetanus vaccines.

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