Microbiology 9- Vaccination against bacterial infections

Question 1

Describe innate immunity

Answer 1

Innate immunity
First line of defence
Does not require exposure to the infectious agent
Is immediate (almost)
Mediated by monocytes and PMNs
Initially an inflammatory reaction

Question 2

Describe Acquired immunity

Answer 2

Acquired immunity
Requires exposure to infectious agents
Takes time to develop
Mediated mainly by lymphocytes (B and T cells)
Other cell types involved, e.g. monocytes and dendritic cells

Question 3

What are vaccines aimed at

Answer 3

Vaccines stimulate both aspects of the immune response but are primarily aimed at eliciting acquired immunity which requires exposure to the infectious agent or its antigens.

Question 4

Describe humoral immunity

Answer 4

Humoral Immunity
directly mediated by antibodies
antibodies are produced by B lymphocytes
Plasma cells (terminally differentiated B lymphocytes) are the primary source of secreted immunoglobulins

Question 5

Describe cell-mediated immunity

Answer 5

Cell Mediated Immunity
not primarily mediated by antibody
mediated by T lymphocytes and NK cells
indirectly other cell types may play a role e.g. macrophages

Question 6

What is important in clearing infections

Answer 6

A combination of humoral and cell-mediated immunity

Question 7

Describe the importance of designing a vaccine that targets the appropriate immune response

Answer 7

Acquired immunity can be divided into two arms: humoral immunity which is mediated by antibodies and cell mediated immunity. It is important that a vaccine stimulates an appropriate immune response. For example, humoral immunity is usually important for preventing septicaemia whereas cell mediate immunity is often important for the prevention of intracellular infections. They are not mutually exclusive with both elements of the immune response playing a role in protection against may diseases.

Question 8

Describe the role of the antibody in immunity to bacterial infections

Answer 8

Role of antibody
Toxin neutralisation, e.g. tetanus, diphtheria, botulism, anthrax etc.
As a focus for complement binding- Ab mediated bactericidal activity
As an opsonin promoting phagocytosis- Ab mediated bactericidal activity
Many bacteria produce exotoxins that have significant effects on the host, e.g. tetanus, botulism, cholera, anthrax, diphtheria, whooping cough etc. Their effects can be neutralised by antibodies binding to active sites or resulting in antibody antigen complexes.

Invasive bacteria and bacteria infecting mucosal surfaces do not always produce exotoxins. Protection against such infections is often mediated by antibodies that kill the bacteria through the classical complement pathway or opsonisation.

Question 9

Describe the role of cell-mediated immunity in immunity to bacterial infections

Answer 9

Role of cell-mediated immunity
Particularly important for eliminating intracellular bacteria, e.g. tuberculosis, typhoid, legionella
interaction of the reactive T lymphocytes and the macrophage is key to clearance of infection

Question 10

List the properties of a good vaccine

Answer 10

Ideally a vaccine:
Stimulates an effective immune response
Is safe and does not cause adverse reactions
Is inexpensive to manufacture and distribute
Is stable
Is easy to administer
Should be simple for both manufacturer and regulatory authorities to control
i.e. a good vaccine provides substantial benefit to health at low cost and low risk

Question 11

What is meant by an effective immune response

Answer 11

It should elicit the correct balance of humoral and cell mediated responses
The immune response should be directed to the relevant site within the host (e.g. the gut in the case of enteric infections).
The immune response should be “functional”. For example, toxin-neutralising antibodies should be able to bind to toxin and neutralise its activity or if bactericidal antibodies are required the antibody should bind both the bacterium and complement.
An effective vaccine would be expected to elicits this response in all (or at least the majority of) vaccinees, give life-long protection without repeated doses, stimulate a boostable response and offer protection against antigenically diverse strains

Question 12

Why is vaccine safety essential and how is this achieved

Answer 12

Vaccine safety is critical as they are given prophylactically to healthy individuals, who should remain healthy after vaccination.
A parenterally administered vaccine must be sterile (although an orally administered vaccine may only need only be free of enteric pathogens).
Vaccine manufacturers follow tightly regulated procedures (e.g. Good Manufacturing Practice; GMP) to ensure that vaccines are manufactured safely and consistently.
Wherever possible they avoid the use of materials of human or animal origin.
The acceptable safety of a vaccine may depend on the recipient. An adult choosing to receive a therapeutic anti-cancer vaccine may be prepared to accept a higher level of risk than a parent taking an infant for routine paediatric vaccination.

Question 13

What is meant by a direct contact

Answer 13

Stopping colonisation leading to infection.

Question 14

What is meant by indirect contact

Answer 14

Herd immunity- prevents pathogen from one organism to the next.

Question 15

Describe herd immunity

Answer 15

Holding the infection in a small part of the population.The term herd immunity refers to the effect of immunity within a population to reduce transmission of the infectious agent, thereby protecting those who are susceptible (i.e. not immune) to the disease. The endemic state reflects a balance between the transmissibility of the infectious agent and the level of immunity in the population. Herd immunity can be modelled mathematically.

Question 16

Do all vaccines result in herd immunity

Answer 16

No

Question 17

Describe Phase 1 trials

Answer 17

Primarily for safety but are often also used to assess immunogenicity
Usually small numbers of adults
entail close clinical monitoring of vaccinees. Data collected might include information on the following: local and systemic reactions, fever, diarrhoea and vomiting and headache etc.

Question 18

Describe phase 2 trials

Answer 18

Primarily for assessing immune response but also used to expand safety database
Typically includes all groups that are likely to use the vaccine
provide an opportunity to investigate the effect of different dose regimes and formulations, examine laboratory assays for correlates/surrogates of protection, and for regulatory laboratories to evaluate the prospective vaccine and validate QC tests. All groups that are likely to use the vaccine include both sexes, a range of ages and different ethnic groups.

Question 19

Describe phase 3 trials

Answer 19

Protection studies, usually placebo controlled double blind trials
provide statistically conclusive data for licensure
Require good disease surveillance
case ascertainment
definition of endpoint
are designed to investigate directly the ability of a vaccine to offer protection against disease. This requires good disease surveillance. Efficacy is the measure of a vaccine to offer protection. Its assessment is scientifically rigorous (e.g. assessed by double blind, placebo controlled trial) and it is required for licensure. Effectiveness studies, sometimes termed phase 4 trials, measure the ability of the vaccine to achieve specific ends. They are scientifically less rigorous, study designs vary and they are not required for licensure. Effectiveness data can help to convince prospective users of the benefits of a vaccine.

Question 20

What are effectiveness trials sometimes referred to as

Answer 20

Phase 4 trials

Question 21

Why is phase 3 sometimes not carried out

Answer 21

Rarer diseases- not enough numbers to generate a high power.

Question 22

Describe vaccine efficacy

Answer 22

Vaccine efficacy is determined in Phase III trials
blinded, placebo controlled

= 1- attack rate in vaccinated group/ attack rate in unvaccinated group
Usually expressed as a percentage.

Question 23

What is Ro related to

Answer 23

There is a relationship between the basic reproduction number R0, vaccine effectiveness and coverage needed to reduce or eliminate disease

Question 24

How can we calculate coverage needed to achieve herd effect

Answer 24

(1-1/R0)/Effectiveness

Question 25

How can the herd effect be calculated

Answer 25

The herd effect is determined post vaccine introduction | = 1- Attack rate in unvaccinated post-introduction/ attack rate in unvaccinated pre-introduction

Question 26

What are the constituents of vaccine formulations

Answer 26

Antigen To stimulate the immune response to the target disease Adjuvant To enhance and modulate the immune response Excipients Buffer, salts, saccharides and proteins to maintain the pH, osmolarity and stability of the vaccine Preservative, e.g. phenoxyethanol, thiomersal etc

Question 27

Why do preservatives sometimes have to be added

Answer 27

Preservatives such as phenoxyethanol or the mercury containing Thiomersal may be added to multidose formulations to prevent growth of microbes once the vial has been punctured. Single dose vials or pre-filled syringes do not usually contain preservative.

Question 28

List the different vaccine antigens

Answer 28

Live attenuated organisms (complex, ill-defined) Killed whole organisms (complex, ill-defined) Purified component vaccines Toxoids Polysaccharide conjugates

Question 29

Describe live attenuated vaccines

Answer 29

These contain mutations that affect the ability of the organism to thrive and/or cause disease in the host. Historically, the mutants were isolated by chemical mutageneisis or multiple passaging of the organism; more recently attenuated isolates have been rationally mutated using targetted molecular methods.

Question 30

Describe killed organisms

Answer 30

Probably the simplest sort of vaccine to produce. The organism is grown and then killed either chemically (e.g. with phenol or formaldehyde) or by heating.

Question 31

Describe component vaccines

Answer 31

The emergence of purified component vaccines has depended upon technological advances since the latter part of the 20th century. These have included advances in physical and chemical methods of separation as well as the development of recombinant DNA techniques, genome sequencing and bioinformatics (for the identification of prospective antigen genes in the genome).

Question 32

Describe DNA vaccines

Answer 32

The antigen gene is cloned in a vector so that it is expressed from a promoter sequence that is functional in the host. Once the DNA is injected, the host expresses the desired antigen and then mounts an immune response.

Question 33

Describe the UK childhood vaccination programme

Answer 33

2, 3 and 4 months old Diphtheria, tetanus, pertussis (whooping cough), polio and Hib One injection MenC One injection Around 13 months old Measles, mumps and rubella (MMR) One injection 3 years and 4 months to 5 years old Diphtheria, tetanus, pertussis (whooping cough) and polio One injection MMR One injection 10 to 14 years old (sometimes neonatal) BCG Skin test, one injection, if needed 13 to 18 years old Diphtheria, tetanus, polio One injection From three years four months onward:- Pre-primary school: DTaP-IPV booster, MMR booster Live attenuated influenza vaccine Girls 12-13 years old: HPV During secondary education: dT-IPV booster, MenACYW

Question 34

Describe the characteristics of the dipetheria and tetanus toxoids

Answer 34

``` Tetanus and diphtheria toxoids chemical inactivation of bacterial exotoxin Simple to produce Relatively pure Safe High protective efficacy very immunogenic appropriate immune response i.e. toxin neutralizing antibodies block activity ```

Question 35

Describe the diptheria toxin

Answer 35

like tetanus toxin is an exotoxin. It is a polypeptide with a MW of 58k and is secreted as a proenzyme which is cleaved into two fragments. Fragment B is responsible for attachment to and penetration of the host cell; Fragment A is the toxic moiety. It is an ADP-ribosylating enzyme that inhibits protein synthesis by blocking eukaryotic elongation factor 2 effectively blocking translation. Like tetanus toxoid, diphtheria toxoid is produced by formaldehyde treatment of culture supernatant.

Question 36

Describe the tetanus toxin

Answer 36

is a neurotoxin causing muscle spasm. It consists of light and heavy chains (MW 50kDa and 100kDa respectively). The light chain is a zinc endopeptidase that cleaves a membrane protein of synaptic vesicles (VAMP). The light chain stops the affected neurons from releasing the inhibitory neurotransmitters causing muscles to contract, so-called tetanus spasm. The toxoid used in vaccines is produced from filtered culture supernatant, which is treated with 40% formaldehyde at 37oC.

Question 37

Describe recent developments of toxoids

Answer 37

More recently toxoids have been developed for the exotoxins including those produced by Clostridium difficile and Pseudomonas aeruginosa though these have yet to be licensed by the regulatory authorities.

Question 38

Describe the Whooping cough

Answer 38

Caused by Bordetella pertussis infecting ciliated epithelium and releasing toxin Condition identified by characteristic convulsive cough Recovery coincides with antibody production

Question 39

Describe the acceptability of the whole cell pertussis vaccine

Answer 39

Whole cell pertussis vaccine is effective efficacy rates typically >90% It has been associated with a number of adverse reactions anaphylaxis prolonged crying febrile siezures acute encephalopathy (now known to be due to mutations within a sodium channel gene) Development of acellular (component) vaccine driven by poor acceptance of the whole cell vaccine

Question 40

Describe the B. pertussis components associated with virulence

Answer 40

``` Attachment to ciliated epithelium filamentous haemagglutinin (FHA) fimbriae pertactin Adherence and complement resistance BrkA Toxins pertussis toxin (PT) adenylate cyclase tracheal cytotoxin heat labile toxin endotoxin ```

Question 41

Describe the acellular vaccines

Answer 41

multicomponent (bi-,tri- and pentavalent fromulations) pertussis toxin, FHA, pertactin, fimbrial antigens 2 and 3 safe and efficacious (75-90%)

Question 42

Describe the whooping cough problem

Answer 42

The acellular vaccine was introduced in the UK in 2004. The vaccine was initially very effective but by eight years later their was an increase in cases and deaths caused by whooping cough. This was addressed in 2013 by the introduction of maternal immunisation but leaves questions about the different immunobiology of the two types of vaccine and how to improve the acellular product.

Question 43

Describe the evidence supporting the hypothesis that aP vaccines fail to provide adequate herd immunity

Answer 43

Acellular pertussis vaccine induces an immune response that is different from natural infection or vaccination with whole cell vaccine. This may explain the resurgence of whooping cough where aP has been widely used. It suggests that aP vaccines need further development. Baboons were vaccinated at 2, 4, and 6m with aP or wP vaccines and challenged at 7m Both groups protected against severe symptoms but … aP vaccinees did not clear the infection faster than naïve animals aP vaccinees were not protected from colonisation Infected aP vaccinees can transmit pertussis to naïve contacts Convalescent and wP-vaccinated animals possess strong Th17 and Th1 memory whereas aP-vaccinated animals induced a Th1/Th2 response

Question 44

Describe Haemophilus influenzae type b

Answer 44

H. influenzae type b causes meningitis and septicaemia in the young. Bacterial surface covered by a polyribosyl-ribitol phosphate capsule. Polysaccharides are poorly immunogenic The Hib component is a conjugate vaccine

Question 45

What improvement was made to the Hib vaccine which controlled the resurgence

Answer 45

Hib-Men C booster introduced at 1yr of age.

Question 46

Summarise the paediatric combination vaccines

Answer 46

``` Examples include Pediacel® (Sanofi) and Infanrix® (GSK) Antigens: Tetanus toxoid Diptheria toxoid Pertussis components: pertussis toxoid, filamentous haemagglutinin, Pertactin fimbriae types 2 and 3 Hib PRP-conjugate Inactivated polio virus types 1,2 and 3 Adjuvant: aluminium phosphate ```

Question 47

Describe the characteristics of polysaccharides as an antigen

Answer 47

The Antigen Usually large and linear Not readily degraded Highly repetitive determinant The Immune Response Predominantly IgM Poor memory effect Low avidity antibody

Question 48

Describe the characteristics of T cell independent antigens

Answer 48

T cell independent antigens like polysaccharides activate mature B cells, in the absence of antigen presentation, by cross-linking immunoglobulin receptors on the cell surface. The resulting immune response is not ideal for vaccination. It is typically characterised by poor immunological memory, low avidity antibodies (no affinity maturation) that are less likely to offer functional protection against disease, and in many cases repeated doses rather than boosting can lead to immunological hyporesponsiveness.

Question 49

Describe conjugate vaccines

Answer 49

Carbohydrate chemically linked to immunogenic protein Sophisticated technology expensive Highly purified components purified saccharide and carrier proteins such as tetanus toxoid, diphtheria toxoid or CRM197 safe simple for licensure and control Very effective when humoral immunity is required long-lived, boostable immunity reduce carriage i.e. offer herd immunity

Question 50

Why are conjugate vaccines important

Answer 50

Conjugate vaccines, in which the saccharide moiety is chemically linked to a protein carrier, overcome the drawbacks of plain polysaccharide vaccines by making them T cell dependent.

Question 51

Describe the steps in producing a conjugate vaccine

Answer 51

Random activation of high molecular weight or partly size reduced polysaccharide Degradation of the polysaccharide to form active functional groups at both terminals Degradation of the polysaccharide to form active functional group at only one terminal

Question 52

Describe how T cell dependent antigens produce an immune response

Answer 52

Naive T cells primed by interaction with antigen presenting cells Requires antigenic stimulation via MHCII-TCR pathway After priming T cells interact with B cells Saccharide specific B cells take up conjugate and present the carrier peptides to T cells via MHCII Activated B cells differentiate into antibody secreting plasma cells and memory B cells

Question 53

Describe the licenced conjugated of Hib

Answer 53

Polyribosyl ribitol phosphate (PRP) conjugated to CRM197 or tetanus toxoid

Question 54

Describe the licenced pneumococcal conjugates

Answer 54

Seven,10- and13-valent formulations

Question 55

Describe the licenced MenC conjugated

Answer 55

α 2-9 linked polysialic acid conjugated to CRM197 or tetanus toxoid

Question 56

What is Menitorix

Answer 56

MenC+Hib booster

Question 57

Describe other conjugates

Answer 57

``` Other conjugates Meningococcal A, C, W, Y conjugates GSK CRM conjugate Menveo™ Pfizer TT conjugate Nimenrix™ In the future Group B streptococcal vaccines ```

Question 58

Describe the Mass vaccination programme with MenC conjugate in the UK

Answer 58

'90s; phased immunisations performed just before winter - given to infants and teenagers; led to significant decrease in Men C, in both vaxxed and non-vaxxed populations. Most cases of Meningitis due to MenB.

Question 59

What was the efficacy and effectiveness of the MenC conjugate vaccine in 2001/2

Answer 59

Efficacy- 93.5% | Effectiveness- 66.8%

Question 60

What does protection of meningococcal disease correlate with

Answer 60

Protection against meningococcal disease correlates with serum bactericidal antibody

Question 61

Describe the need for a later MenC conjugate vaccine

Answer 61

Transmission of meningococci occurs primarily among young adults 4-valent MenACYW vaccine introduced to address increase in MenW disease.

Question 62

Describe pneumococcal disease

Answer 62

Streptococcus pneumoniae is significant cause of meningitis and septicaemia worldwide It is also an important cause of mucosal infections, e.g. pneumonia and otitis media

Question 63

What are the majority of the serotypes of pneumococcal disease determined by

Answer 63

More than 90 serotypes determined by capsular polysaccharide Antibiotic resistance associated with some serotypes vaccines are made against more common strains - have many-serotype plain (unconjugated) vaccines as well as conjugate vaccines for younger populations; concerns about serotype replacement

Question 64

What vaccines are available for pneumococcal disease

Answer 64

Pneumovax II™, 23-valent plain (unconjugated) polysaccharide vaccine Prevenar 7™, Prevenar 13™ and Synflorix™ conjugate vaccines

Question 65

Describe Pneumococcal conjugate vaccine efficacy

Answer 65

Cases of pneumonia significantly reduced where there was a positive radiograph from 10.1 to 8.3 per 1000 person-years Estimated efficacy 17.7% (95% CI: 4.8 to 28.9) against pneumonia Reduction in cases of otitis media by 7-9%

Question 66

.Describe the impact of pneumococcal conjugate vaccine on different serotypes

Answer 66

Pneumococcal conjugate vaccines (PCV 7 and 13) have had a substantial impact on IPD caused by vaccine serotypes. Replacement disease with non-vaccine serotypes remains a concern. Rapid increase in some highly virulent non-PCV serotypes may compromise the benefits of the programme. 8,12F, and 9N are a particular problem- nearly all replacement disease occurs in adults.

Question 67

Describe meningococcal outer membrane vaccines

Answer 67

OMVs are released spontaneously by meningococci in vivo and in culture They contain all the protein antigens usually associated with the OM Vaccines are produced by detergent extraction to reduce endotoxin content Hyper-producing mutants have been isolated

Question 68

What may be a potential issue with OMVs

Answer 68

Could be reactive against own antigens- but research has shown that we are pretty tolerant to OMVs- but there is still a concern.

Question 69

What is a key thing to remember about OMVs

Answer 69

Vaccines only offer good protection against the homologous strain

Question 70

Describe the Reverse Vaccinology Approach

Answer 70

Sometimes Pasteur's principles of Isolate, Inactivate and Inject don't work. Use computer simulated programmes to predict candidate antigens (genome sequence) test recombinant antigens (DNA vaccines) on rats.

Question 71

Give some examples of candidate antigens for MenB

Answer 71

Factor H binding protein (fHbp) Neisseria adhesin (NadA) Heparin binding protein (Nhbp) Bexsero™ contains OMVs from strain NZ98/254 enhanced with three component antigens found by scanning genome Clinical trials show it to be safe and immunogenic Licensed by EC Jan 2013 and rolled out in the UK infant programme from Sep 2015 Trumenba™ a component vaccine consisting of two lipidated recombinant Factor H binding proteins - not yet licensed in the UK These are non-capsular antigens.

Question 72

Describe the initial impact data of Bexsero

Answer 72

Estimated from vaccine eligible children after two doses Effectiveness 82·9% (95% CI 24·1–95·2) Incidence ratio reduction 0·50 [95% CI 0·36–0·71]; p=0·0001 37 cases vs average 74 cases before introduction

Question 73

Describe the BCG vaccine against TB

Answer 73

Attenuated strain of Mycobacterium bovis. Serial passage, 231 times over 13 years (1908-1921) Phenotypic changes: rough/dry to moist/smooth Genotypic changes: loss of RD1 region encoding 9 proteins

Question 74

Discuss the evidence surrounding the efficacy of the BCG vaccine

Answer 74

Cannot be answered definitively Vaccination programmes instituted at the same time as social, economic and public health improvements Generally accepted that it prevents severe childhood TB and leprosy Variation in field trials of BCG Trial methodology Vaccine variation (strain, dose, potency) Regional differences in TB strains New candidate vaccines are in the research pipeline recombinant modified vaccinia virus expressing antigen 85A

Question 75

Describe the Typhoid vaccines

Answer 75

Vivotif ® live attenuated vaccine based on strain Ty21a galE mutant of S. typhi Ty2 isolated by NTG mutagenesis formulated in enteric-coated capsules Vi polysaccharide (TyphimVi ® and Typherix ®) Offered to those travelling to typhoid endemic areas Only suitable for >2 year olds Conjugates in development

Question 76

Describe the killed whole cell parenteral vaccine for cholera

Answer 76

poor efficacy short-lived protective response strain specific

Question 77

Describe the killed whole cell oral vaccine for cholera

Answer 77

good efficacy in cholera endemic area (Vietnam trials) oral delivery safe >85% show >4-fold rise in vibriocidal antibodies (<3% in controls) protective efficacy 66% after two doses WHO mediated technology transfer

Question 78

Describe the Dukoral vaccine for cholera

Answer 78

killed whole cell + CtxB oral vaccine drink formulation (3 doses at weekly intervals, booster every 2 years) may also protect against ETEC

Question 79

What are adjuvants

Answer 79

Adjuvants are a key element of effective vaccines. They potentiate the immune response (humoral, cellular or both).

Question 80

Describe how adjuvants can be used as delivery systems

Answer 80

``` Delivery systems, usually a depot of antigen which is slowly released mineral salts surface active agents synthetic microparticles oil-water emulsions liposomes ```

Question 81

Describe how adjuvants can be used to potentiate the immune response

Answer 81

``` potentiating immune response by interacting with PAMPs - stimulating innate immune response. Toxins and lipids Nucleic acids (CpG) Peptidoglycan Carbohydrates Peptides Cytokines and hormones ```

Question 82

How are adjuvants licenced

Answer 82

As part of the vaccine formulation

Question 83

Describe how can we manipulate PRR and TLRs

Answer 83

Different receptors- different cytokines- different immune response- can target appropriate one.

Question 84

Describe risk-benefit analysis

Answer 84

Need to protect the vulnerable patient Public health perspective (herd immunity) Protect the patient by immunising close contacts Live vaccines need particular consideration Decision on whether to vaccinate depends on the nature of the immunodeficiency and the vaccine. Can 'ring-fence' individual- vaccinate close relatives.