Vaccine preventable diseases 13-16 Flashcards
Describe the global burden of mortality and morbidity attributable to vaccine preventable disease
Vaccines are an effective intervention to decrease morbidity and mortality due to the infection in under 5’s.
It is dependent on several factors and only effective if given:
- Immunological factors
Politics, peace and resources
Environmental factors
What is the definition of a vaccine?
An antigenic substance prepared from the causative agent of a disease or a synthetic substitute, used to provide immunity against one or several diseases
Describe the progression of infant immunity and how this affects risk of infection
Infants are born with passive immunity from the mother but immunological maturation increases significantly after 1 year
- Th2 cells prevalent initially with IL-4 + IL-10 as not to reject mother and baby
- Th1 cells prevalent after 1 year –> babies won’t respond well to vaccines
Pragmatically vaccine infants younger than 1 years old as mother will be more likely to attend hospital due to maternal leave.
Give 4 examples of diseases affected by global health factors
1) Measles - virus which causes a rash due to Vit A deficiency. In areas of conflict and rural areas there is 0 coverage which then spreads to refugee camps. Increased coverage in India but decrease in S Sudan and Syria due to lack of infrastructure and government instability
2) Tetanus - toxin mediated by Clostridium tetani. Increased prevalence in areas w/ high risk birthing practices e.g. using animal faces to cover placental cord; many countries offer tetanus vaccine but not in the UK as high neonatal mortality
3) Pertussis - whooping cough; high risk in neonatal period –> neonatal apnoea
4) Haemophilus Influenza B - Very effective vaccine but takes 9-11 years to introduce into LICs vs HICs
5) Poliomyelitis - reported in Yemen and S Sudan due to not maintaining coverage
What are the characteristics that a vaccine preventable disease must have?
- Known causative agent
- Not hyper-variable/stable agent
- Antigens that are different to humans
- Known mechanism of infection/disease
- Antigen must induce stable/long last immunity
What are the characteristics that a vaccine preventable disease should have?
- Minimal reservoir/host range
- Natural immunity protects
- Acute not chronic infection
- Culturable causative agent
- Animal agent
What are the characteristics of an ideal vaccine?
Completely safe East to administer Single dose, needle-free Cheap Stable Active against all variants Life-long protections
What are the characteristics of an eradicable infectious disease?
Safe + effective vaccine Genetically stable target No animal reservoir Eliminates persistent infection, or persistently infected host can't transmit Easy and reliable diagnostics
What causes variability in vaccine efficacy? (x2)
Host factors
Vaccine characteristics
What are the host factors that cause variability in vaccine efficacy?
Age Co-morbidity: including frailty/function Prior exposure Time since vaccination Underpinning infection Maternal immunisation
What are the vaccine characteristics that cause variability in vaccine efficacy?
Mode of delivery Live-vs inactivated Vaccine composition Addition of adjuvant Match to circulating strains
What causes variability in global vaccine efficacy?
Differences in host genetics Circulating strain differences Underpinning infections Vaccine batches Logistics
What is herd immunity?
A form of indirect protection from infectious disease that occurs when a large % of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune.
What is the definition of R0?
Basic reproduction number = the number of cases one case generates on average over the course of their infectious period
What is the definition of R1?
Effective reproduction number = a population will rarely be totally susceptible to an infection in the real world; reflects the number of susceptible cases
What is herd immunity threshold?
(Pc) The proportion of individuals that need to be vaccinated to control the incidence of infectious disease. This increases as R0 increases.
Why is herd immunity important in vaccine preventable diseases?
By vaccinating children for example, you protect against infants and the elderly who may be immunocompromised. It is also important to carry out targeted vaccination.
What is targeted vaccination?
Targeting groups of people who have an increased risk of transmitting a disease. Risk of spread can vary with behaviour e.g. STI/partner number, sex - if you vaccinate these people, you can get elimination for a lower overall vaccination rate e.g. HPV.
Age is a key determinant - can reduce proportion vaccinated.
What are the 5 different types of vaccines?
(CRIDL) Conjugate vaccines Recombinant protein vaccines Inactivated toxoid vaccines Dead pathogen Live, attenuated vaccine
What is the MOA and example of conjugate vaccine?
1) Polysaccharide coat component is coupled to an immunogenic ‘carrier’ protein
2) Protein enlists CD4 help to boost B cell response to the polysaccharide
E.g. Streptococcus pneumoniae
What is the MOA and example of a recombinant protein vaccine?
1) Induces classic neutralising antibodies
E.g. Hep B Surface Antigen (HbSAg)
What is the MOA and example of an inactivated toxoid vaccine?
1) Chemically inactivated form of toxin e.g. tetanus toxoid
2) Induces antibody
3) Antibody blocks the toxin from binding the nerves
E.g. Tetanus toxoid
What is the MOA and example of a dead pathogen vaccine?
1) Pathogen chemically killed
2) Induces antibody and T Cell responses
Eg. influenza split vaccines
What is the MOA and example of a live attenuated vaccine?
1) Pathogen attenuated by serial passage which leads to loss of virulence factors
2) Replicate in situ which triggers innate response + boosts the immune response
E.g. BCG
Give examples of 5 potentially preventable diseases?
SARS MRSA Dengue HIV Malaria TB
What are the challenges to vaccine development?
Wrong type of protection
High pathogen variation - strain replacement e.g. Influenza
Natural infection is not protective - Cryptic antigens; evasion from immune response e.g. malaria
Vaccine induced disease
Flawed translation from animal models
Vaccinating people with poor immune response (heterogeneity) i.e. not applicable to whole population
What are the socio-economic barriers of developing new vaccines?
Injection safety Logistics/cold chain Development issues: time, cost of vaccine development is high, cost of the product Weak public health systems Public expectation of risk-free vaccines
What are the concerns of sub-population about vaccines and vaccine programmes?
Complex + context-specific –> varies across time, place and vaccines
3 C’s model of vaccine hesitancy:
Complacency = Lack of perceived need/ value for vaccine
Convenience = access to vaccine
Confidence = level of trust in vaccine, provider or process
SAGE working group determinants of vaccine hesitancy: contextual influences, individual/social influences/vaccine and vaccination-specific issues
What is the WHO definition of vaccine hesitancy?
Delay in acceptance or refusal of vaccines despite availability of vaccination services
What is the vaccine hesitancy continuum?
Unquestioning acceptance Accept cautiously Hesitant Delay some vaccines Refuse all vaccines
What is the psychometric paradigm?
The public tend to judge risks not by fatalities but by the characteristics of risk
Describe the HPV vaccine case in Denmark.
In 2012, a number of cases of postural Orthostatic tachycardia syndrome (POTS) and similar syndromes in young women were reported + was hypothesised that it was linked to the HPV vaccine that was started in 2008/9. A TV documentary was subsequently made and this dramatically decreased HPV coverage across the country due to social media as well. Coverage dropped from 80-90% to 20-30%.
In 2015, the European Medicines Agency (EMA) reviewed the literature and found no evidence for a causal association. Later studies showed that the girls reporting those syndromes were more frequent healthcare users so factors other than the vaccine probably caused it.
Coverage slowly increased from 27% in June 2016 to 73% in June 2018 (Lynge et al., 2018). But unfortunate that those girls could have been vaccinated when they were sexually naive as they would have been 15-16 where one third of them would have already by sexually active.
Describe the HPV Vaccine case study in Japan.
In 2013 an adverse event following immunisation claim was released causing a dramatic drop in vaccine uptake in Japan. A preliminary + allegedly fraudulent mouse study showed that the vaccine caused brain damage and was spread by the media + unconfirmed video reports of girls in wheelchairs and having seizures after getting immunised. Anti-vaccine groups also blamed the vaccine for causing chronic pain + heart + neuro issues.
Government then suspended any proactive recommendations for the HPV vaccine despite finding no evidence to support claims - demonstrates impact of governments.
Turned out the brain that was being shown on TV wasn’t even the mouse brain that was injected with the HPV vaccine. The mice used were genetically modified to produce auto-antibodies naturally during aging. Serum full of these antibodies was taken from the mice and sprayed on brain sections of normal mice and photographed to show brain damage.
Vaccine coverage has decreased dramatically from 70% (2013) to less than 1% (2017).
What are the interventions shown to increase vaccination in healthcare providers?
Free vaccine
Easy access
Educational activities, reminders or incentives
Opt outs or mandatory immunisation policies
Peer vaccination
People turn to GP and pharmacies most so more likely to vaccinate if healthcare providers recommends it.
What is an AEFI?
Adverse Event Following Immunisation
Healthcare workers need to be well trained to address serious AEFI’s: investigation, causality assessment, communication
Effective system for monitoring safety of vaccines; safety signals need to be well investigated and responded to. When AEFIs are well handled the risk of vaccine hesitancy is minimised.
What are the 3 things to address vaccine hesitancy?
Identify susceptible population groups
Diagnose drivers + barriers to immunisation
Design and evaluate evidence-based interventions
