How do vaccines work?

Vaccines train the immune system to recognise specific pathogens by introducing an antigen — part of or a weakened/inactivated pathogen, or (in mRNA vaccines) instructions to make a viral protein — that triggers an immune response without causing disease. The immune system forms memory cells so that future encounters produce faster, stronger responses. This principle has been proven for over 200 years since Jenner's smallpox vaccination.

Yes. Vaccines are among the most rigorously tested medical interventions and are continuously monitored after approval. Before any vaccine reaches the public it undergoes years of clinical trials in tens of thousands of people. Serious adverse events do occur but are extremely rare — far rarer than the diseases vaccines prevent. The risk-benefit analysis overwhelmingly favours vaccination for virtually all recommended vaccines.

What is herd immunity and when is it achieved?

Herd immunity occurs when enough of a population is immune that a pathogen cannot spread efficiently, protecting even those who are not immune. The threshold varies by transmissibility: measles requires ~95% immunity; polio ~80-85%. Vaccine-induced herd immunity is safer than through natural infection, which causes disease, disability and death.

Who are zero-dose children and why do they matter?

Zero-dose children are those who have received no vaccines at all — not even DTP1. In 2023, 14.3 million children fell into this category, disproportionately in Nigeria, India, DRC, Ethiopia, Pakistan and Afghanistan — often in conflict-affected areas, remote communities or urban slums. They face the highest risk of vaccine-preventable death and are the central equity challenge of IA2030.

What is the Immunization Agenda 2030?

IA2030 is the global immunization strategy endorsed by the World Health Assembly in 2020. Its five priorities to 2030: leaving no one behind (zero-dose children); strong immunization systems; vaccine supply and innovation; sustainability; and research. Its headline target is 90% coverage with all national-schedule vaccines by 2030, alongside disease elimination milestones.

Why does the flu vaccine change every year?

Influenza viruses mutate rapidly through antigenic drift. WHO's Global Influenza Surveillance and Response System (GISRS) monitors circulating strains and makes recommendations twice yearly for Northern and Southern hemisphere season vaccines. Because influenza evolves, last year's vaccine may not protect against this year's dominant strain — which is also why a universal influenza vaccine is a major research priority.

What are the new vaccines approved in recent years?

The last decade produced a remarkable vaccine expansion: RTS,S (Mosquirix) and R21/Matrix-M — the first licensed malaria vaccines; TAK-003 (Qdenga) — a dengue vaccine; RSV vaccines (Abrysvo, Arexvy) for older adults (2023); mRNA COVID-19 vaccines demonstrating unprecedented development speed; and mpox vaccine deployment in 2022. Cancer therapeutic vaccines are in advanced trials.

What causes vaccine hesitancy?

WHO SAGE identified three clusters: confidence (distrust in safety, efficacy or the system); complacency (low perceived disease risk); and convenience (access, affordability, supply barriers). Misinformation amplifies all three. Effective responses combine trusted community messengers, tailored communication, healthcare provider training and structural access improvements.

How did COVID-19 affect childhood vaccination?

COVID-19 caused the largest sustained childhood immunization decline in 30 years. In 2020-2021, 25 million children missed routine vaccines. Clinics closed, health workers were redeployed and caregivers stayed home. The result was surging measles outbreaks and resurgence of other vaccine-preventable diseases. DTP3 coverage recovered to 84% in 2022, still below the pre-pandemic 85%.

What is GAVI and what does it do?

GAVI, the Vaccine Alliance, is a public-private partnership that increases immunisation access in low-income countries. It pools demand to negotiate lower vaccine prices, co-finances vaccination programmes and supports health system strengthening. Since 2000, GAVI has helped vaccinate over 1 billion children and is estimated to have prevented 18 million future deaths.

What is CEPI and what is it doing?

CEPI (Coalition for Epidemic Preparedness Innovations) finances and coordinates vaccine development for epidemic and pandemic threats. Founded in 2017 after Ebola, it supports candidates for pathogens on the WHO priority list. Its 100 Days Mission aims to compress new vaccine development from years to 100 days — demonstrated with COVID-19 vaccine development.

How does GMJ News cover vaccines?

GMJ News follows WHO SAGE recommendations, GAVI programme updates, immunization coverage data and vaccine-hesitancy research. Georgia has a strong national immunization programme, and vaccination policy in the South Caucasus is a recurring subject in the Georgian Medical Journal. All safety and efficacy claims are sourced to WHO, regulatory agencies or peer-reviewed trials.

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Vaccines

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Vaccination is among the most effective interventions in the history of medicine: WHO estimates immunization has saved about 154 million lives over the past 50 years — roughly six lives every minute (EPI at 50, Lancet 2024). The evidence keeps strengthening: HPV vaccination reduces cervical precancer by close to 90% in girls vaccinated early (England cohort, Lancet 2021), and measles vaccination alone has averted an estimated 60 million deaths since 2000. The WHO Immunization Agenda 2030 now targets the millions of zero-dose children still unreached.

Key messages

Life-saving impact

Vaccination has saved an estimated 154 million lives over 50 years (1974-2024) — more than any other health intervention (Shattock et al., Lancet 2024).

Zero-dose crisis

14.3 million children received zero vaccines in 2023 — the most vulnerable to vaccine-preventable disease. Most live in fragile states, urban slums or hard-to-reach communities.

COVID-19 setback

The pandemic caused the largest sustained decline in childhood vaccination in 30 years. 25 million children were under-vaccinated in 2021, driving measles and other outbreak surges.

Immunization Agenda 2030

The global framework IA2030 targets reaching zero-dose children, sustaining elimination gains and integrating vaccines into universal health coverage by 2030.

New vaccines

The COVID-19 pandemic accelerated mRNA technology. Licensed malaria vaccines (RTS,S, R21), RSV vaccines, the first dengue vaccine and Qdenga represent a new era of vaccine development.

Vaccine hesitancy

Hesitancy — driven by confidence, complacency and convenience barriers — is a recognised global health threat. Misinformation and distrust require targeted communication strategies beyond traditional messaging.

Key statistics

154M

lives saved in 50 years

Lancet 2024

14.3M

zero-dose children (2023)

WHO/UNICEF

84%

global DTP3 coverage (2022)

WHO/UNICEF

25M

under-vaccinated children (2021)

WHO/UNICEF 2022

20+

diseases preventable by vaccine

WHO

$1 = $44

return on investment

WHO/World Bank

Global DTP3 vaccination coverage (%) 2000-2022 — WHO/UNICEF estimates

Source: WHO/UNICEF Joint Estimates of National Immunization Coverage. DTP3 = third dose diphtheria-tetanus-pertussis.

Glossary of key terms

Herd immunity
WHOIndirect protection when a sufficient proportion of a population is immune — through vaccination or prior infection — that the pathogen cannot spread efficiently, protecting even the non-immune.

Zero-dose children
GAVI/WHOChildren who have received no vaccines at all — not even the first DTP dose. They are the most at-risk from vaccine-preventable diseases and the primary equity target of IA2030.

SAGE
WHOStrategic Advisory Group of Experts on Immunization — the authoritative WHO body that formulates global immunization recommendations guiding national programmes.

Cold chain
WHO/UNICEFThe temperature-controlled supply chain keeping vaccines effective from manufacture to administration. Cold chain failures cause significant vaccine wastage, particularly in LMICs.

mRNA vaccine
FDA/EMAA vaccine using messenger RNA to instruct cells to produce a protein (e.g. SARS-CoV-2 spike) that triggers an immune response. No live virus or DNA involved. Proven with COVID-19 vaccines and in development for influenza and cancer.

Adjuvant
EMA/FDAA substance added to some vaccines to enhance the immune response to the antigen. Aluminium salts have been used since the 1930s; newer adjuvants like AS01 enable stronger responses with smaller doses.