Immunisation and Vaccination

Immunisation Strategies and Public Health

Programs
 Routine Childhood Immunisation: Most countries have established schedules
ensuring infants and children receive multiple vaccine doses for key diseases
(e.g., DTP, MMR, polio, rotavirus, hepatitis B).
 Catch-Up Immunisation: Special strategies for individuals who missed
scheduled doses, including school-based immunisations and community
outreach campaigns.
 Booster Campaigns: Some vaccines require additional doses as immunity can
wane over time, such as tetanus, pertussis, and certain COVID-19 vaccines.
 Travel Immunisation: Travellers may need vaccines against region-specific
diseases (e.g., yellow fever, typhoid, Japanese encephalitis).
 Occupational Immunisation: Healthcare workers, laboratory staff, and others
at risk may require extra immunisations (e.g., hepatitis B, rabies).
 Mass Vaccination Campaigns: Used in response to outbreaks or for
elimination/eradication efforts (e.g., meningitis, measles, polio).
 Ring Vaccination: Targeted immunisation of contacts around a case, used for
diseases like smallpox and Ebola.

Immunisation Schedules:
Age Vaccine(s) Diseases Prevented
Birth BCG, Hepatitis B Tuberculosis, Hepatitis B
2 months DTP, IPV, Hib, PCV, Diphtheria, Tetanus,
Rotavirus Pertussis, Polio,
Haemophilus influenzae
b, Pneumococcal,
Rotavirus
6 months Influenza (annual from Influenza, Hepatitis B
6m+), Hepatitis B (if
required)
1 year MMR, Varicella Measles, Mumps,
Rubella, Chickenpox
4-6 years DTP, MMR, IPV Diphtheria, Tetanus,
Pertussis, Measles,
Mumps, Rubella, Polio
Mechanisms of Immunity: Active vs. Passive
Immunisation
 Active Immunisation: Involves exposure to antigen (vaccine or infection),
leading to the production of memory B and T cells. This creates long-term,
adaptive immunity.
 Passive Immunisation: Involves the transfer of ready-made antibodies (e.g.,
maternal antibodies via placenta, immunoglobulin injections). Provides
immediate but short-lived protection. Used for rapid response to infection or
toxin exposure (e.g., rabies, tetanus, snake bites).
 Artificial vs. Natural: Both active and passive immunity can arise naturally
(infection, maternal antibodies) or artificially (vaccination, antibody therapy).

The Immune Response and Vaccination

 Primary Response: First exposure to antigen; lag phase before antibody
production; usually IgM antibodies appear first, followed by IgG.
 Secondary (Anamnestic) Response: Subsequent exposure; rapid, robust
antibody production (mainly IgG); forms the basis for booster vaccinations.
 Cellular Immunity: Vaccines also stimulate T cells (helper and cytotoxic),
which are critical for fighting intracellular pathogens like viruses and some
bacteria.
 Memory Cells: Surviving B and T lymphocytes ensure a faster, stronger
response upon re-exposure to the pathogen.

Diagram: (Description) Line graph showing antibody titre over time after primary and
secondary exposure to antigen, highlighting the more rapid and higher response
after the secondary exposure.
Types of Vaccines: Mechanisms, Examples, and
Properties
Type Example(s) Mechani Advantages Limitations
sm
Live MMR, BCG, Weakene Strong, long- Not suitable for
attenuated Oral Polio d but live lasting immunity; immunocompromi
(Sabin) pathogen often needs 1-2 sed; storage
stimulates doses challenges
full
immune
response
Inactivated Polio (Salk), Killed Safe for Weaker response;
(killed) Hepatitis A pathogen; immunocompromi may need
induces sed; stable in boosters
immune storage
response
without
replicatin
g
Subunit/conjug HPV, Hib, Key Low side effects; Expensive;
ate Pneumococ antigens targeted immunity sometimes
cal only, often weaker response
linked to
carrier
proteins
Toxoid Tetanus, Inactivate Highly effective; Requires boosters
Diphtheria d toxin minimal risk of
triggers disease
antibody
productio
n
mRNA COVID-19 Delivers Rapid Requires cold
(Pfizer, genetic development; storage; long-term
Moderna) code for elicits both data still emerging
antigen; antibody and cell-
host cells mediated
produce responses
antigen

Global Impact and Successes of Immunisation

 Eradication: Smallpox eradicated (1980); polio nearly eliminated globally.
 Control: Dramatic reductions in measles, diphtheria, tetanus, pertussis,
rubella, and other diseases in countries with high vaccine coverage.
 Herd Immunity: High vaccination rates protect unvaccinated individuals and
those who can’t be vaccinated (e.g., due to immune disorders).
  Economic Benefits: Reduced burdens on healthcare systems, improved
workforce productivity, and fewer disability cases.
 Outbreak Prevention: Rapid response vaccination campaigns can halt
epidemics (e.g., Ebola, yellow fever).
Diagram: (Description) Bar chart comparing global incidence rates of measles, polio,
and diphtheria before and after mass vaccination introduction.

Monitoring Vaccine Safety and Effectiveness

 Pre-licensure Clinical Trials: Vaccines undergo phased human trials (Phase I-
III) to assess safety, immunogenicity, and efficacy.
 Post-licensure Surveillance: Ongoing monitoring (pharmacovigilance) via
systems like VAERS (US), Yellow Card (UK), to identify rare adverse events
and ensure long-term safety.
 Batch Testing: Each vaccine lot is quality controlled for potency, purity, and
sterility before distribution.
 Effectiveness Studies: Population studies and case-control analyses evaluate
real-world impact and identify waning immunity or breakthrough cases.

Innovations and Future Directions in Vaccinology

 Needle-free Delivery: Jet injectors, microneedle patches, and oral/nasal
vaccines aim to increase coverage and reduce discomfort.
 Universal Vaccines: Efforts to develop vaccines that protect against all strains
of pathogens (e.g., universal influenza or coronavirus vaccines).
 Personalised Vaccines: Cancer vaccines and precision vaccinations tailored
to individual immune genetics.
 Reverse Vaccinology: Use of computational genomics to identify novel
antigens for vaccine targets.
 Therapeutic Vaccines: Vaccines not just for prevention, but as treatment (e.g.,
for chronic infections or cancer).

Diagram: (Description) Flowchart of vaccine development: antigen discovery →

preclinical studies → clinical trials → regulatory approval → post-market
surveillance.

Societal and Economic Factors Affecting

Vaccination Programs
 Legislation: Some nations enforce mandatory vaccination for school entry or
healthcare work; others rely on voluntary uptake.
  Communication Strategies: Addressing vaccine myths, misinformation, and
building trust is essential for public acceptance.
 Global Health Initiatives: Gavi, WHO, and UNICEF run major vaccination
programs and support low-income countries.
 Supply Chain Management: Ensuring timely, reliable delivery and storage,
especially during pandemics or conflicts.
 Equity: Closing gaps in vaccine access due to geography, conflict, poverty, or
marginalisation.

Case Study: Measles Elimination in the Americas

 Background: Measles, a highly contagious viral disease, caused widespread
morbidity and mortality in the Americas until the late 20th century.
 Strategy: The Pan American Health Organization (PAHO) implemented an
intensive regional vaccination program, combining mass immunisation
campaigns and routine childhood vaccinations.
 Implementation: Health workers conducted door-to-door campaigns, mass
media informed the public, and catch-up campaigns targeted older children
and adults.
 Success: By 2002, the Americas were declared measles-free, marking a
historic achievement in public health.
 Lessons: High vaccination coverage, surveillance, rapid outbreak response,
and strong political commitment were crucial.
 Ongoing Challenges: Global travel, vaccine hesitancy, and importation of
measles have caused sporadic outbreaks, highlighting the need for sustained
immunisation vigilance.
 DNA Vaccines: Use of plasmid DNA to elicit robust cellular and humoral
immunity; currently in trials for infectious diseases and cancers.
 Vector Vaccines: Use harmless viruses (e.g., adenovirus) to deliver antigen
genes; examples include Ebola and COVID-19 vaccines.

The fight against measles in the Americas was characterized by unprecedented

regional collaboration and innovation. In the 1980s, measles remained a major
cause of childhood death and disability, especially in countries with limited
healthcare resources. Recognizing the urgent need for action, PAHO and member
countries developed a multifaceted approach that went beyond standard
immunisation.

Enhanced Strategies
 Catch-Up Campaigns: Initial nationwide efforts targeted all children aged 9
months to 14 years, regardless of prior vaccination status. This created a
 foundational level of population immunity and interrupted endemic
transmission.
 Keep-Up Activities: To maintain high coverage, routine immunisation services
were strengthened in every country, ensuring each birth cohort was protected.
 Follow-Up Campaigns: Every 3-5 years, periodic campaigns were conducted
to vaccinate new groups of susceptible children who had missed previous
rounds or were too young at the time.

Surveillance & Rapid Response

A cornerstone of the initiative was robust, laboratory-backed surveillance. Health
authorities established a network for rapid case detection and confirmation.
Whenever suspected measles was reported, outbreak investigation teams were
mobilised to contain the spread through targeted vaccination and public awareness.

Public Engagement and Political Will

Mass media—radio, television, and print—played a crucial role, educating families
on the importance of vaccination and dispelling myths. Political leaders at all levels
publicly endorsed the campaigns, making immunisation a civic priority and securing
necessary resources.

Results and Impact

Thanks to these coordinated efforts, measles cases in the Americas plummeted from
hundreds of thousands annually in the early 1980s to zero endemic cases by 2002.
The last confirmed endemic case was reported in Venezuela in 2002. This
achievement represented not just the elimination of measles, but a dramatic
reduction in childhood morbidity and mortality, and substantial healthcare savings.

Results and Impact

The coordinated strategies led to a remarkable decline in measles cases in the
Americas, falling from hundreds of thousands annually in the early 1980s to zero
endemic cases by 2002. The last confirmed endemic case was reported in
Venezuela in 2002. This achievement represented not only the elimination of
measles but also a substantial reduction in childhood illness and death, as well as
significant healthcare savings.

Building Broader Vaccine Resilience

Strengthening Routine Immunisation Systems
The measles elimination initiative had far-reaching benefits for overall immunisation
programmes. By enhancing cold chain infrastructure, improving the logistics of
vaccine storage and delivery, and standardising training for health workers, countries
created durable systems that supported the introduction of new and essential
vaccines, such as those for polio, rotavirus, and HPV.

Integrating Health Services with Vaccination

Campaigns often served as a platform to provide other preventive health services.

For example, vitamin A supplementation and deworming initiatives were integrated
into vaccination days. This comprehensive approach improved children's nutrition
and overall health, maximising the value of each outreach effort.

Innovations in Vaccine Delivery

To reach children in remote or underserved communities, innovative approaches

were adopted. Mobile immunisation clinics, temporary vaccination posts in schools
or community centres, and outreach by community health workers ensured no
population was overlooked. These innovations also set precedents for future public
health responses, including pandemic preparedness.

Addressing Vaccine Hesitancy

As elimination drew closer, authorities recognised the importance of community trust.

Targeted communication, engagement with local leaders, and culturally sensitive
educational materials helped address fears and misconceptions, ensuring that high
coverage could be maintained and that new generations would continue to be
protected.

Global Collaboration and Knowledge Sharing

The strategies, data, and lessons learned from the Americas became a resource for
global measles elimination efforts. International partnerships between governments,
health agencies, and non-governmental organisations promoted rapid information
exchange and technical assistance, accelerating progress in other regions.
Economic and Social Benefits

Eliminating measles led to fewer days lost from school and work, less strain on
health facilities, and an overall healthier, more productive society. The investment in
vaccines returned significant long-term economic gains through reduced healthcare
costs and increased opportunities for children to thrive.

Adapting to New Challenges

The evolving landscape of global health, including mobility and migration, requires
ongoing adaptation. The systems and strategies that succeeded in measles
elimination now serve as models for combating other vaccine-preventable diseases,
ensuring resilience even as new threats emerge.
These expanded efforts demonstrate that the legacy of measles elimination is not
only the absence of disease, but also the creation of stronger, more responsive, and
more equitable health systems across the Americas and beyond.

Legacy and Current Challenges

The success in the Americas became a blueprint for global measles elimination.
However, the region’s status remains fragile. Imported cases, often from regions with
ongoing transmission, pose a constant threat. Vaccine hesitancy and gaps in
coverage have led to sporadic outbreaks in recent years, underscoring the need for
vigilance, responsive health systems, and ongoing community engagement.