Understanding modern-day vaccines: what you need to know
https://www.tandfonline.com/doi/full/10.1080/07853890.2017.1407035
Abstract
Vaccines are considered to be one of the greatest public health achievements of the last century. Depending on the biology of the infection, the disease to be prevented, and the targeted population, a vaccine may require the induction of different adaptive immune mechanisms to be effective. Understanding the basic concepts of different vaccines is therefore crucial to understand their mode of action, benefits, risks, and their potential real-life impact on protection. This review aims to provide healthcare professionals with background information about the main vaccine designs and concepts of protection in a simplified way to improve their knowledge and understanding, and increase their confidence in the science of vaccination (
Supplementary Material).
- KEY MESSAGE
- Different vaccine designs, each with different advantages and limitations, can be applied for protection against a particular disease.
- Vaccines may contain live-attenuated pathogens, inactivated pathogens, or only parts of pathogens and may also contain adjuvants to stimulate the immune responses.
- This review explains the mode of action, benefits, risks and real-life impact of vaccines by highlighting key vaccine concepts.
- An improved knowledge and understanding of the main vaccine designs and concepts of protection will help support the appropriate use and expectations of vaccines, increase confidence in the science of vaccination, and help reduce vaccine hesitancy.
1. Introduction
Vaccines are one of the greatest public health achievements of the last century and are estimated to save 2–3 million lives each year [
1]. They have successfully eradicated smallpox and have greatly reduced the incidence of several major diseases such as polio and measles [
1,
2]. Licensed vaccines are now available to prevent over 30 different infectious diseases, several of which can be combined into single vaccines or administered at a single vaccination visit [
1]. In this review, we highlight the different vaccine designs and illustrate them through various examples to give non-experts a basic understanding of vaccines and concepts of prevention.
1.1. What is the aim of vaccination?
The aim of vaccination is to induce a protective immune response to the targeted pathogen without the risk of acquiring the disease and its potential complications.
1.2. How do vaccines work?
Vaccines, like natural infections, act by initiating an innate immune response, which in turn activates an antigen-specific adaptive immune response [
3]. Innate immunity is the first line of defence against pathogens that have entered the body. It is established within a few hours but is not specific for a particular pathogen and has no memory [
4]. Adaptive immunity provides a second line of defence, generally at a later stage of infection, characterized by an extraordinarily diverse set of lymphocytes and antibodies able to recognize and eliminate virtually all known pathogens. Each pathogen (or vaccine) expresses (or contains) antigens that induce cell-mediated immunity by activating highly specific subsets of T lymphocytes and humoral immunity by stimulating B lymphocytes to produce specific antibodies [
3]. After elimination of the pathogen, the adaptive immune system generally establishes immunological memory. This immunological memory – the basis of long-term protection and the goal of vaccination – is characterized by the persistence of antibodies and the generation of memory cells that can rapidly reactivate upon subsequent exposure to the same pathogen [
3].
1.3. What you need to know about vaccine design and concepts?
Vaccine design has made significant advances in the last century, evolving from serendipity to a more rational design due to advances in understanding immunological mechanisms and technology [
1]. Depending on the biology of the infection and the disease to be prevented, a vaccine may require the induction of different humoral (i.e. antibodies) or cell-mediated (i.e. T cells) adaptive immune mechanisms to be effective. Understanding the mode of action of vaccines is therefore important to predict their efficacy, their safety profile, and their expected benefit for the vaccinated individuals and the general population.
Although vaccines are mostly seen as tools for individual protection, vaccines can also protect unvaccinated populations by reducing the rate of person-to-person transmission and limiting the risk for individuals to be exposed. This indirect protection, called herd or community protection, requires that a large portion of the population (75–95% depending on the disease), or a special group that plays a key role in transmission of the disease, is vaccinated [
5,
6]. Herd protection is often essential for the success of vaccination programs, such as for measles [
7]. Similarly, vaccination of pregnant women can also indirectly protect infants in their first months of life through transfer of maternal antibodies from the mother to the foetus across the placenta [
8]. This concept has been successfully established for tetanus, influenza and pertussis [
8].
In contrast to the generally well-known pharmacological effects of different drugs, the differences between vaccine types are also important but less well understood by many healthcare providers. Different vaccines targeting the same pathogen can rely on very different concepts (
Figure 1), each having advantages and limitations (Table 1). Choosing a particular vaccine therefore can depend on several factors such as the level of protection, the expected mode of action, the characteristics of the subject, or the disease elimination strategy. Many healthcare providers have not received sufficient education on vaccines, which could contribute to vaccine hesitancy among healthcare providers or patients [
9].
Figure 1. Different types of vaccines. Vaccines can be produced using different processes. Vaccines may contain live attenuated pathogens (usually viruses), inactivated whole pathogens, toxoids (an inactivated form of the toxin produced by bacteria that causes the disease), or parts of the pathogens (e.g. natural or recombinant proteins, polysaccharides, conjugated polysaccharide or virus-like particles).
(Much more at above url -- including detailed discussion of all the vaccine types)
