Immunisation

VaccinesImmunisation programmeImmunisation strategy

Importance of immunisation

The most effective intervention (most effective public health intervention after clean water)

Globally, 3 million deaths per year and 750,000 children disabled by vaccine-preventable infections

1 in 4 children (~30 million) have no access to vaccination for 6 EPI diseases (measles, polio, pertussis, diphtheria, tetanus, TB)

Types of Immunisation

Passive– Temporary protection, e.g. immunoglobulin (specific protein

substance produced by plasma cells to fight infection)– Taken from infected individuals, good for people whose

immune systems are not strong

Active– Longer term protection leading to the formation of

antibodies

Exploring new delivery systems e.g. aerosols, ‘edible’ vaccines, topical

Types of vaccine

Live vaccine– Live but weakened organism or virus; replicates in the host– Single dose, long duration of immunity, may revert to

virulent strain and can cause disease in immuno-suppressed

– E.g. oral polio vaccine, MMR, yellow fever Inactivated vaccines

– Killed micro-organism or their toxins or subunit vaccines– Conjugate (a vaccine where a polysaccharide antigen is

chemically joined with a protein molecule to improve the immunogenicity of the polysaccharide)

– Multiple doses & booster, short immunity and stable– E.g. DTaP/IPV/Hib, Men C, Hepatitis B Vaccine (HBV) and

Hepatitis A Vaccine (HAV)

Vaccines

Aim of vaccine is to induce long term immunological memory

Interrupts transmission of the infection (for infections transmitted person to person)

Contra indications to immunisation

Very few real contra-indications

1. A confirmed anaphylactic reaction to a previous dose of the vaccine

2. A confirmed anaphylactic reaction to a component of the vaccine

3. Immunosuppression (live vaccines) Check Green Book for national

recommendations; WHO recommendations & manufacturer’s data sheet

Vaccine failure

Primary– An individual fails to make an adequate immune

response to the initial vaccination

Secondary failure– An individual makes an adequate immune

response initially but then immunity wanes over time

Designing/developing a Vaccination Programme

Is there a suitable vaccine?

Is there a need?

The need for a vaccination programme depends on:

1. Disease epidemiology – Disease incidence– Age distribution of

disease– Disease trends– Disease complications– Mortality

2. Vaccine type safety and efficacy

3. Aim, cost & benefit of programme

4. Cultural attitudes and practices

5. Political expedience

6. Facilities available for delivery

7. Provision of trained primary care providers

8. Population accessibility

Vaccine Trials

Pre-license Phase 1 studies Safety studies, in health adult volunteers (10-20)

Phase 2 studies Assess common reactions and immunogenicity – in target population (100-200)

Phase 3 studies Protective efficacy – in target population (large)

Post-license Phase 4 studies Surveillance, to detect (rare) adverse events

Vaccine Trials

May also be pharmo-economic studies at phase 3 (i.e. cost benefit analysis, cost effective analysis)

Phase 4 surveillance is needed to detect rarer adverse events due to variability in preparation, storage and vaccines are used in different groups than pre-license studies.

Evaluation - Targets

Coverage Targets set by WHO, DoH and Local

EPI European Region targets are – high coverage (over 95% overall; over 90% in all

geopolitical areas) – Better surveillance– Laboratory support

Factors associated with low coverage

1. Socio-demographic variables Deprived, inner city areas Mobile families (i.e. don’t register with GP

or miss appointments) Larger family size Children with chronic illness Ethnic status

Factors associated with low coverage

2. Personal Variables– Parental attitudes to disease, to vaccine– Professional knowledge and attitudes to disease, to

vaccine– Misconceptions of contra-indications

3. Media stories4. Health service variables

– Poor co-ordination– Unclear responsibility– Access to guidelines and protocols– Accuracy of information– Computerisation, default lists

Developing immunisation strategy

Mass immunisation or selective immunisation Selective:

– travel, e.g. HAV – occupational, e.g. HBV for health care workers– Chronic disease, e.g. pneumococcal – outbreak, e.g. HAV

Developing immunisation strategy

Mass immunisation’s aim is to eradicate (e.g. small pox)

– Disease and its casual agent have been removed worldwide

eliminate (e.g. polio)– Disease has disappeared from one region but

remains elsewhere contain (e.g. Hib)

– Point at which the disease no longer constitutes a ‘significant public health problem’

Prioritising vaccines

WHO Global expanded Programme on immunization (EPI)

– Diphtheria– Tetanus– Pertussis– Measles– TB– Poliomyelitis– Hepatitis B– Yellow fever

Countries decide their own immunisation programmes depending on incidences of diseases within the countries

Other priority diseases in EU are rubella and mumps and Hib

Aim for WHO European Region to eliminate measles in every country by 2010.

Implementation of vaccination policy

Choice of policy (mass or selective) Publish recommendations (‘green book’) License vaccine Purchase vaccine Media campaign and start giving

vaccinations

Delivery of programme

Central roles

1. Choice of vaccine policy (DH following recommendations from JCVI)

2. Publication of policy and recommendations (Green Book)

3. Licensing of vaccine (MHRA)

4. Control of vaccine (NIBSC)

5. Purchase of vaccine (DH)

6. Storage and distribution of vaccine (Farillon on behalf of DH)

Delivery of programme

Local contract from commissioner (PCT) Provider

– GP practice (practice nurse)– Community clinics (CMOs, health visitor)– Others (e.g. occupational health)

UK immunisation service is excellent– Birth notification enters child on child health system in each

district– Consent for vaccination obtained by health visitor– Scheduled for vaccination by child health system (or GP)– Invitation and appointment to parent and list of appointments

to clinic or GP– Record of vaccinations given entered on child health system

Systems for delivery elsewhere

Compulsory vaccination e.g. France, Italy Physicians must deliver vaccines e.g.

France, Italy Separation of prescribing and dispensing,

e.g. France

UK initiatives on immunisation coverage

1986 – district immunisation co-ordinators 1990 – GP contract (good practice payment) Others: special immunisation clinics, target

health promotion campaigns, national and local education material

Surveillance

Surveillance of vaccine delivery needs to follow vaccine policy

Surveillance of vaccine preventable disease1. Disease incidence

2. Vaccine coverage

3. Serological surveillance

4. Adverse events

Objectives of surveillance

Pre-implementation– Estimate burden– Decide strategy

Post-implementation– Monitor effectiveness, predict impact

Nearing elimination– Identify pockets of susceptible– Certification process

1. Disease incidence (routine)

Main sources of data– Statutory notification

No lab confirmation/case definition required so poor for assessing efficacy; incomplete so low sensitivity as disease declines

– Laboratory reporting– Death registration

Other sources– Hospital episodes – Sentinel physician reporting

More complete data linked to denominator so good for burden– Paediatric surveillance

Complete, stimulated reporting so good for detailed follow up

2. Surveillance of vaccine coverage

COVER Computerised child health register in each area; quarterly

request to immunisation co-ordinator; national and regional aggregation of data published in CDR; SHA/PCT data fed back at regional and local levels

Uses: 1. Evaluate vaccination programme2. Feedback to public health professionals3. Targeting areas of low coverage4. Vaccine effectiveness/efficacy5. Outcome measurement (risk factors for vaccine failure; impact on

age and other groups)6. Modelling, planning and policy

Surveillance Cont’d

3. Serological Surveillance Representative samples of

target population, can be ad-hoc or routine

Opportunistic samples Collected annually for 1-15

years; five yearly for adults; age and sex coded

4. Adverse events following immunisation (AEFI)This is any event that follows immunisation that negatively affects health

passive reporting (i.e. yellow card)

active reporting – used for rare serious adverse events; British Paediatric Surveillance Unit – aseptic meningitis following MMR eventually led to withdrawal of Urabe vaccine