Immunisations Flashcards
What are the objectives of immunisation
To protect individuals from a disease (either from infection or from mortality)
To protect populations
To achieve herd immunity - to stop transmission
Eradication of disease
Decrease severity of disease - reducing hospitalisation
Indirect protection - vaccinating mother to protect baby e.g. whooping cough
To protect selected high risk groups
What is the difference between eradication and elimination
Elimination: removal from an area (no longer endemic) - but can still get imported cases.
Eradication - no cases
Difference between vaccination and immunisation
Vaccination = to give a vaccine - may not result in immunity
Immunisation - to artificially confer immunity
2 mechanisms of immunisation
Active
Passive
Different types of vaccines
Live unattenuated
Live attenuated
Killed whole organisms
Disrupted toxin
Antigenic components from organisms
Manufactured virus like particles
Conjugated vaccine
Example of live unattenuated vaccine
Original cow pox innoculations - body generates immunity to small pox not just cow pox (and cow pox doesn’t make them that sick)
Examples of live attenuated vaccines
MMR
BCG
Oral Polio vaccine
Example of killed whole organism vaccine
Injectable polio
Example of disrupted toxin vaccine
Tetanus toxoid
Example of antigenic components from organisms vaccine
Flu
Hep B
Covid19
example of manufactured virus like particles vaccines
HPV
What is a conjugated vaccine
combines a weak antigen with a strong antigen as a carrier so that the immune system has a stronger response to the weak antigen
(particularly in vaccines for children e.g. HIB)
Why is eradication difficult to achieve
Expensive
Has to be a global effort
Only works if vaccines stop transmission rather than reducing severity
Needs peace (not war)
Needs political will
What are nasal vaccines good for
Reducing airborne transmission
What factors effect susceptibility to disease
Immunity - previous natural infection or previous immunisation
Age - immature immune systems and waning immunity (the older you get the less able you are to produce a non specific response - rely on memory and targeted response
Immunocompetence - immune deficiency syndromes, immunosuppressive treatments, steroids, intercurrent infection
Why will 100% personal protection never be achieved with immunisation
<100% Vaccine efficacy due to:
- handling
- temperature
- optimal age for vaccination
- Boosters (lack of completing course)
- Optimal dose etc.
- Mutation of pathogen
- effective administration
<100% vaccine uptake due to:
- public perception
- misinformation
- accessibility
- culture
- production - enough
- religion (vaccines containing pork etc.)
- medical conditions/contraindications preventing immunisation
What does R0 depend on
Organism characteristics: infectivity, duration of infectiousness
Population characteristics: Mixing patterns, demographics, population density
What is the effective reproduction number (R)
the average number of secondary infections produced by a typical infective agent.
In a homogenously mixing population where s is the proportion susceptible: R=R0xs
What is the epidemic threshold?
If R>1, the number of cases increases
If R <1, the number of cases decreases
R=1 is the epidemic threshold.
To achieve elimination we need to maintain R<1
What is the critical proportion susceptible (s*)
The threshold at R=1, defines the critical proportion susceptible, s*
1=R0 x s
S* = 1/R0
What variable effects herd immunity
the greater the infectivity (reproductive rate) of a disease, the higher the immunisation rate needed to achieve herd immunity
Herd Immunity Threshold (H)
H = 1-S*
so
H=1-1/R0
Measles has one of the highest herd immunity thresholds (92-95%) whereas influenza has one of the lowest (33-44%)
What is vaccine efficacy (VE)
AR (unvaccinated)
x100
(AR = attack rate)
Decision making process for deciding whether to implement a new immunisation programme
- Disease burden (is it a PH problem) - no. of cases, morbidity, mortality
- Is immunisation the best strategy for controlling the disease (is there another way and then analyse cost, benefit, effectiveness, safety, feasibility, practicality of each method compared to immunisation)
- What will be the net impact of introducing a new vaccine (impact on disease burden - vaccine effectiveness; vaccine safety (adverse effects, monitoring systems, vaccine damage, compensation schemes)
- How well is our current immunisation programme working? (will introduction of a new vaccine make things better or worse, fit in with current schedule)
- How much disease will be prevented (depends on age-specific disease burden in relation to age of immunisation, vaccine effectiveness & coverage)
- what are the possible negative effects of the new vaccination programme? (vaccine risk, possibility of programme errors, risk in strategy, vaccines interfering with each other)
- what resources are needed
- what is the impact on public perception (will adding new vaccine damage perception of immunisation)
- is the vaccine a good investment (cost of introduction - one off and ongoing costs, economic analysis: cost-benefit compared to other interventions, opportunity cost)
What to consider when implementing vaccines (short answer)
- Cost benefit analysis
- demand/need
- infrastructure
- acceptability
- purpose of vaccination
What to consider when implementing a new immunisation programme
- Who to vaccinate (depends on aim - to protect vulnerable, contain outbreak or eradicate disease); group with greatest morbidity/mortality; window of opportunity for prevention (e.g. preexposure); optimum effectiveness; vaccine efficacy in different age groups
- How to implement (Pilots, phased introduction, global immunisation)
- When to vaccinate (greatest impact on disease burden e.g. seasonal diseases; things to do to maximise uptake e.g. term time if school aged, multiple vaccines for rapid protection of most vulnerable etc.)
Examples of international immunisation programmes
EPI - expanded programme on immunisation
GPEI - global polio eradication initiative
GAVI (global alliance for vaccines and immunisation)
COVAX
Role of WHO for immunisations
- makes recommendations for policy
- supports less able countries with strategy implementation
- works through the international health regulations
Diphtheria
Caused by Corynebacterium diphtheria
Primarily infects the throat and upper airways
Produces a toxin affecting other organs
2 types:
- disease of throat and tonsils
- skin ulcers especially in tropical countries
most cases in unvaccinated children
fatal in 5-10%
Tetanus
Clostridium tetani
produces a toxin that causes painful muscle contractions, making it hard to open the mouth and swallow (lockjaw)
Neonatal and maternal tetanus = most common & serious
Mortality reducing due to TTCV (tetanus toxoid containing vaccine)
MNTE: Maternal & Neonatal Tetanus Elimination Initiative, launched 1999 (immunisation, clean deliveries & surveillance)
Polio
Viral. V infectious.
Mostly effects children <5
Person to person spread, mainly faecal-oral or sometimes contaminated food/water
Intestine –> nervous system –> paralysis
1/200 irreversible paralysis. 5-10% die.
Cases dramatically reducing - oral polio vaccine multiple doses for children
in 2020 only Afghanistan and Pakistan were still polio-endemic
Measles
Viral. Airborne transmission. Prior to vaccine in 1963 major epidemics every 2-3 years. Most deaths = complications –> most common in <5 and >30.
Blindness, encephalitis, severe diarrhoea & dehydration, ear infections, pneumonia
Severe more likely in malnourished, insufficient vitA, immunocompromised (HIV/AIDS etc.)
95% in LICs
Measles vaccines - one of the best buys in PH
Haemophilus Influenza B (HiB)
Bacterial, transmitted through resp tract.
Severe pneumonia, meningitis etc. <5.
2-3 million serious, 386000 deaths p.a.
Needs prompt lab investigation prior to Abx.
Abx resistance increasing
Vaccine - only PH tool: in >100 countries so far.
Hib conjugate vaccine recommended (available monovalent or combined with DTP and others)
Hepatitis B
Viral.
Transmission: blood & sex
Life threatening & can lead to chronic liver disease & > death from liver cirrhosis & liver cancer
2billion infected
Vaccine 95% effective preventing infection & chronic consequences
Only given to high risk groups in UK atm.
Yellow Fever
Caused by flavivirus. Mosquito vector.
Cases severely underreported.
Varies from mild fever –> fatal multi-organ failure
200,000 cases & 30,000 deaths p.a.
Vaccine: life long immunity, used in travellers & outbreak.
Mosquito control programmes - lapsed in some areas
Strategy to Eliminate Yellow fever Epidemic (EYE) by GAVI, WHO, UNICEF etc to face challenging epidemiology, resurgence of mosquitos, increased risk of urban outbreaks and spread. Aims to protect at risk populations, prevent international spread, contain outbreaks rapidly
Vaccines at 8 weeks
Diphtheria, tetanus, pertussis (whooping cough), polio, Hib, hep B
MenB
Rotavirus
Vaccines at 12 weeks
Diphtheria, tetanus, pertussis, polio, Hib, hep B
Pneumococcal
Rotavirus
Vaccines at 16 weeks
Diphtheria, tetanus, pertussis, polio, Hib and hepatitis B
MenB
1 year old vaccines
Hib, MenC
Pneumococcal
MMR
MenB
Eligable children each year from September vaccine
Influenza
~3 years 4 months vaccines
Diphtheria, tetanus, pertussis, polio
MMR
Boys and girls aged 12-13 vaccines
HPV
14 years vaccines
Tetanus, diphtheria, polio
Meningococcal A,C,W,Y
65 years old vaccine
Pneumococcal & Shingles
> 65 years annual vaccine
influenza
70-79 years vaccine
shingles
Expanded Programme on Immunisation (EPI)
Launched following success of smallpox vaccine. Aims to ensure vaccination for all children <1.
Measles, whooping cough, diphtheria, tetanus, polio, TB now also vitamin A, HBsAG B (HepB), Hib, Yellow fever
Strategies to achieve global vaccination targets
Integrate vaccination with primary healthcare services
Expand vaccination coverage to eligible population
Ensure regular supply of potent vaccines
Strengthen the cold chain
Training & capacity building of health personnel
Promote community participation
Incorporating health education
Ensure logistic support
Monitoring & evaluation
Research
What is the vaccine cold chain pathway
Need to maintain the same temperature throughout the chain
- Manufacturer
- National storage facility
- Regional hospital
- Health centre
- Vaccination outreach
Challenges in implementing vaccination programmes (globally)
Cold chain management
Education (public awareness/support, culture, suspicion of the west
Mistrust
Corruption
Cost
Lack of skills in healthcare workers
Lack of training
Supply chain
Access - vaccination on a market day, difficult to access communities etc
6 Objectives of the global vaccine action plan
- All countries commit to immunisation as a priority
- individuals & communities understand the value of vaccines & demand them as their right and responisbility
- benefits of immunisation equitably extended to all people
- strengthen immunisation systems as part of a well functioning health system
- ensure immunisation programmes have sustainable access to predictable funding, supply, & innovative technologies
- Country, regional, and global research and development innovations maximise benefits of immunisation.
