CHAPTER 2. LITERATURE REVIEW
This thesis aimed to explore factors associated with vaccine reactogenicity and further understanding of the immunological mechanisms underlying these events. Therefore the focus of the literature review was potential mechanisms of, and factors associated with, commonly reported AEFI and reactogenicity. In finding that there is very little literature specifically addressing these issues, the review was extended to discuss factors which may contribute to AEFI in order to support a model of biological processes. Not included in this review is literature on vaccine safety and safety monitoring systems nor overall vaccine safety.
Searches were initially conducted using Medline, EMBASE and PubMed and Google Scholar. Key words included but not restricted to were:
Adverse events following immunisation; reactogenicity; vaccine reactions; local reactions; systemic reactions; vaccine; immuni[s]ation; vaccination; subcutaneous; injection technique; injection administration; pain; erythema; induration; swelling; local reaction and vaccine; fever vaccine and adverse event; fever and immune[z]ation; arthus reaction; cytokine; fever; serum sickness; alumin[i]um immunology; lipopolysaccharide; muscle and antigen presentation; skeletal muscle; skeletal muscle immunology; inflammatory cytokine/s; stress psychological and immunity; exercise and immunity; deltoid muscle.
The outline of chapter two is illustrated in Figure 2-1.
Vaccine formulation and reactogenicity
Vaccine form and function
Vaccine form has evolved greatly since the early practices of variolation against smallpox which possibly date back as early as 8th Century India and 10th Century China as referred to in chapter 184.108.40.206 34 The vaccines commonly in use on international immunisation schedules today can broadly be classified into three main categories:
Live attenuated (weakened) Inactivated or whole dead Subunit Within each there may be sub categories and many vaccines are multivalent, containing a combination of different types.
Live attenuated vaccines: Live vaccines include vaccines against measles, mumps, rubella, varicella and rotavirus. Traditionally live vaccines have been weakened by serial passage in cell culture until a level of attenuation has been reached, rendering the organism immunogenic and minimally reactogenic. Today the precise genetic mutations that are responsible for attenuation must be demonstrated for any new vaccine.35 Live vaccines do not require adjuvant and cannot contain preservative. Once administered the attenuated organism replicates systemically in its target tissue and generates an immune response qualitatively similar to wild infection.35 AEFI following live vaccines are more likely to be systemic rather than local.36
Inactivated or whole dead vaccines: “Inactivated” generally refers to viral vaccines, such as polio vaccines, which have been chemically inactivated but still retain their general form. Whole dead refers to bacterial vaccines such as whole cell pertussis vaccine where the organism has been killed. These vaccines almost always contain adjuvant.35
Sub Unit vaccines: Sub unit vaccines contain fragments of the target organisms. The fragments may be obtained using a range of technologies. Traditionally these vaccines were made by degrading the original organism and purifying the components of interest or inactivating toxins into toxoids. Polysaccharide antigens can be purified and used on their own or conjugated to a protein carrier. More recently antigens of interest, such as hepatitis B surface antigen and human papillomavirus viral-like particles, have been produced recombinantly using genetic engineering.35
It is the immunogens or antigens and the adjuvants that have intimate interaction with the immune system. However there are a range of other ingredients that may be added to a vaccine formulation in addition to these core ingredients. There may also be residual substances remaining from the manufacturing process. Preservatives, stabilisers, buffers, surfactants and residuals are briefly outlined below followed by an in depth discussion on adjuvants.
Preservatives: Preservatives are added to minimise the risk of microbial contamination of the vaccine, particularly of multi-dose vials. Until recently the most commonly used preservative in vaccines was thiomersal, a mercury based product. Due to a move to reduce mercury exposure from all sources thiomersal was removed from many vaccines and none of the vaccines on the New Zealand schedule contains this product.37 Today phenoxyethanol is the most commonly used preservative and phenol, which is used infrequently.
Stabilisers: Stabilisers inhibit chemical reactions and prevent components separating or sticking to the vial during transport and storage. Examples of stabilisers include sugars such as lactose and sucrose, amino acids such as glycine and monosodium glutamate and albumin (human or bovine). Gelatin, which is partially hydrolysed collagen (usually bovine or porcine) is added to some vaccines as a stabiliser.
Buffers: Buffers serve to resist changes in pH, adjust tonicity and maintain osmolarity.
The most commonly used buffer is sodium chloride.
Surfactants/emulsifiers: Surfactants or emulsifiers are wetting agents that alter the surface tension of a liquid and lower the tension between two liquids, in a similar manner to the way detergents act. An example is Polysorbate 80 (Tween®).
Residual products: Residual products will depend on the manufacturing process used which may have involved cell culture fluids, egg proteins, yeast, antibiotics such as neomycin or streptomycin or inactivating agents such as formaldehyde. These substances are often measured as parts per million and parts per billion or nanograms in the final vaccine formulation.
Vaccine formulation is such that it induces a robust immune response, and the ideal vaccine will do this with minimal adverse side effects. None the less the role of vaccine is to interact with the immune system and will, by design, often cause symptoms characteristic of inflammation. There are two key components of a vaccine that are most likely the cause of reactogenicity (antigen and adjuvant) and there are several other components that are sometimes included in a formulation in order to minimise reactions (such as sodium chloride to control pH).
Most vaccines commonly in use are inactivated or subunit vaccines and most of these contain adjuvant. In contrast, live vaccines (such as measles, mumps and rubella) do not contain adjuvant and induce their immunity systemically. The processes of immune induction between live and subunit vaccines are quite different with the response to live vaccine mimicking the natural disease process more closely. Live vaccines such as MMR®II (measles mumps and rubella vaccine) are less locally reactogenic than subunit vaccines.
As the role of a vaccine is to introduce antigen to the immune system and the role of adjuvant is to enhance the process the next section will focus on adjuvant, primarily aluminium adjuvant as until very recently it was the only adjuvant licensed for use in humans. Since this thesis was begun two new adjuvants have joined the market (MF59® and ASO4®). As the first principles are the same for these proprietary adjuvants the relevance of their actions will be summarised at the end of this section
Aluminium adjuvants, history and reactogenicity
‘Adjuvant’ is derived from the Latin ‘adjuvare’ which means ‘to help’.
Many of the vaccines used globally contain aluminium-based adjuvants. Aluminium adjuvants have played a vital role in enabling basic vaccines such as tetanus, diphtheria and pertussis to be used effectively. A key part of the development of these “classical’ vaccines was the emergence of adjuvant technologies that have continued to be used in vaccines for decades.38
Purpose of Adjuvants
Immunological adjuvants are generally considered to be materials that are added to vaccines with the intent of:
- Potentiating the immune response so that a greater amount of antibody is produced
- Reducing the amount of antigen required and
- Reducing the number of doses required.
Many vaccine antigens are not particularly immunogenic on their own and it is necessary to add substances which can in some way assist in an effective immune response to them. There are many such substances which vary widely in their nature from microbial motifs (microbial molecular patterns) to nano particles. Until recently aluminium salts have been the only vaccine adjuvants licensed for human use. This use extends over 70 years and is associated with an excellent safety profile.39 40
History of aluminium adjuvants
In 1925, Ramon showed that the antibody response to tetanus and diphtheria was increased by injecting the two vaccines together with a range of other compounds such as agar, tapioca, lecithin, starch, oil, saponins and breadcrumbs (from Clements).41
In 1926 Glenny, Pope, Waddington and Wallace showed that when a solution of potassium aluminium sulphate was added to diphtheria toxoid, a precipitate was formed. Depending on the added amount of aluminium, the remaining filtrate no longer contained toxin – suggesting the toxin had been bound to the aluminium. Injecting guinea pigs subcutaneously with these precipitations resulted in a greater antibody response compared with injection with untreated toxoids. The authors interpreted the adjuvant effect as being due partly to the delay of absorption of antigen from the local site of injection, resulting in prolonged stimulation of cells within the regional lymphatic glands, and also partly due to the production of a local granuloma containing antibody-producing plasma cells.42 This work laid the foundation for the next 70 years for using aluminium in the manufacture of vaccines. Later, work in 1931 considered the release of toxoid from the injected aluminium precipitate was prolonged so that antigen liberated later could act as a secondary type stimulus.43
Experiments described from 1935 discussed how three day old aluminium nodules from guinea pigs were excised, macerated and planted into recipients who subsequently developed antibodies. Such granuloma were found still antigenically active after seven weeks with potency declining over a period of 48 days.43
The theory that the increased activity conferred by aluminium was due to a secondary response from the delayed release of antigen from the injection site was criticised in 1950 when Holt proposed that antigen was excluded from the physiological interior of the animal because of its gradual encapsulation. Presumably Holt was suggesting that because the antigen was encapsulated it was hidden from the immune system. Landsteiner (1945) suggested that many factors might play a role in the activities of alum precipitated antigen including slow absorption, delayed removal of antigen, the particulate state and consequent phagocytosis of the particles by antibody-producing cells, and the stimulation of cell activity (sourced from White).44
Production of antibody was found by White to proceed partly within the regional lymph glands and partly in the granulation tissue surrounding the nodule which develops at the site of injection. The antibody was noted to first appear in the lymph gland, only becoming apparent in the granuloma from 14 days onwards. Antibody-containing plasma cells were demonstrated in the local granuloma for up to seven weeks and antibody-containing cells in the regional lymph glands reached maximum numbers at two weeks following injection and decrease thereafter to a few cells at five weeks.4
Early proposed mechanisms of action
In 1971 it was found that when a small dose of radioactively labelled protein was injected subcutaneously into the paw of a mouse that 98-99% left the limb within 24 hours and only a fraction remained in the draining lymph node. It was thought that by slowing down the escape of antigen from the injection site and therefore lengthening the period of contact of antigen with macrophages and other antigen-presenting cells that the immunogenic stimulus would be greatly enhanced. Early work showed that alum-precipitated antigens retained the antigens in high concentration at the site of injection, releasing it slowly, and that antibody producing plasmacytes (B-cells) developed in greater numbers over a longer period of time when the antigen was precipitated to alum. It was further noted that a local granuloma developed at the injection site hosting large numbers of antibody producing B-cells, further contributing to the synthesis of antibody. This granuloma was considered a necessary requirement for effective adjuvant action. It has been noted that it is important to administer aluminium-containing vaccines intramuscularly because granuloma formation in subcutaneous tissue can undergo necrotic breakdown causing cyst and abscess formation.4
CHAPTER 1. INTRODUCTION
1.1 BACKGROUND TO RESEARCH
1.2 RESEARCH AIMS AND OBJECTIVES
1.3 OUTLINE OF THESIS
CHAPTER 2. LITERATURE REVIEW
2.1 VACCINE FORMULATION AND REACTOGENICITY
2.2 VACCINE DELIVERY FACTORS AND REACTOGENICITY
2.3 HOST FACTORS AND POTENTIAL FOR REACTOGENICITY
2.4 DEFINING AND DESCRIBING LOCAL VACCINE REACTOGENICITY
2.5 CONCLUSIONS FROM THE REVIEW OF LITERATURE
CHAPTER 3. SECONDARY ANALYSIS OF THE NZ MENINGOCOCCAL B VACCINE SCHOOLBASED CLINICAL TRIAL
3.2 STUDY DESIGN AND DATA
3.3 METHOD FOR SECONDARY ANALYSES
CHAPTER 4. RESULTS FROM SECONDARY ANALYSES OF MENINGOCOCCAL B TRIAL DATA
4.1 SAMPLE POPULATION
4.2 INJECTION PAIN AND REACTOGENICITY OUTCOMES
4.3 CONSIDERATION OF FINDINGS FROM SECONDARY ANALYSIS OF MENINGOCOCCAL B TRIAL DATA
CHAPTER 5. FACTORS ASSOCIATED WITH REACTOGENICITY ‐ THE FAR TRIAL
5.1 RATIONALE FOR APPROACH FOR THE FAR TRIAL
5.2 AIM, HYPOTHESES AND OBJECTIVES OF THE FAR TRIAL
5.3 STUDY POPULATION AND SAMPLE
5.4 DATA COLLECTION AND MEASUREMENT TOOLS
5.5 STUDY MATERIALS
5.6 SEROLOGY – PROCEDURES AND MATERIALS
5.7 STUDY PROCEDURES
5.8 SAMPLE SIZE
5.9 STATISTICAL ANALYSES AND PRESENTATION
CHAPTER 6. RESULTS FROM THE FAR TRIAL
6.1 AIMS OF CHAPTER
6.2 PARTICIPANT RECRUITMENT AND FLOW
6.3 BASELINE DATA
6.4 PRIMARY OUTCOMES
6.5 SECONDARY OUTCOMES FROM THE FAR TRIAL
6.6 SUMMARY OF THE FINDINGS FROM THE FAR TRIAL
CHAPTER 7. IS THERE A RELATIONSHIP BETWEEN LOCAL REACTIONS AND IMMUNOGENICITY?
7.1 AIMS AND OBJECTIVES
7.2 STUDY DESIGN AND DATA
7.3 DATA ANALYSIS
7.5 CONSIDERATION OF FINDINGS
CHAPTER 8. DISCUSSION
8.1 SYNOPSIS OF KEY FINDINGS FROM NZ MENINGOCOCCAL B VACCINE STUDY AND
8.2 STRENGTHS AND LIMITATIONS OF THIS THESIS
8.3 COMPARISON AND CONSISTENCY WITH RELEVANT FINDINGS FROM OTHER
PUBLISHED STUDIES .
CHAPTER 9. CONCLUSIONS
9.1 GENERAL CONCLUSIONS
9.2 CLINICAL IMPLICATIONS
9.3 RESEARCH IMPLICATIONS AND RECOMMENDATIONS
9.4 POLICY IMPLICATIONS AND RECOMMENDATIONS
CHAPTER 10. APPENDICES
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