The Role of Immunisation in Disaster Risk Prevention

When disasters strike-whether earthquakes, floods, cyclones, or armed conflicts-the immediate aftermath often creates conditions ripe for infectious disease outbreaks. Overcrowded shelters, contaminated water sources, disrupted healthcare systems, and malnourished populations combine to put survivors at heightened risk for vaccine-preventable diseases. Immunisation becomes a critical tool not just for individual protection but for preventing secondary health crises that can claim more lives than the initial disaster itself.

Understanding immunisation in disaster contexts 🔗

Immunisation works by stimulating the body’s immune system to develop resistance against specific infectious diseases. Vaccines introduce a weakened or inactivated form of a pathogen, prompting the body to produce antibodies without causing the actual disease. This acquired immunity protects individuals and, when coverage is sufficiently high, creates herd immunity that shields entire communities-including those who cannot be vaccinated.

In disaster settings, this protection becomes especially vital. Displaced populations, including refugees and internally displaced persons, face elevated risks for diseases like measles, cholera, typhoid, and diphtheria. The breakdown of routine health services during emergencies often means vaccination programmes are disrupted precisely when they’re needed most. Children who miss scheduled vaccines and adults living in crowded conditions without access to clean water become highly susceptible to outbreaks.

The World Health Organization emphasises that vaccine-preventable disease outbreaks during humanitarian emergencies have highlighted the need for comprehensive, evidence-based frameworks to guide vaccination decisions. The primary goal is to determine whether delivering vaccines to specific populations during an emergency would result in an overall reduction in deaths and disease burden.

At-risk populations requiring priority protection 🔗

Certain groups face disproportionate risks during disasters and require priority consideration in immunisation planning. Children under five years of age are particularly vulnerable to measles, which can spread rapidly in emergency shelters and displacement camps. Pregnant women require protection against tetanus and other diseases that threaten both maternal and infant health. Healthcare workers on the frontlines of disaster response need vaccination to remain healthy and continue providing care. Elderly individuals and those with chronic conditions often have weakened immune systems and higher susceptibility to severe disease outcomes.

Communities with historically low vaccination coverage are especially at risk. When disasters displace these populations into crowded settings, previously controlled diseases can resurge explosively. The Immunization Agenda 2030 strategic framework specifically addresses the need to ensure service delivery during emergencies and in communities affected by conflict, disaster, and humanitarian crisis.

Immunisation strategies in disaster response 🔗

Emergency vaccination responses typically follow one of two primary approaches: mass vaccination campaigns or targeted vaccination. Each strategy has distinct advantages, limitations, and appropriate applications depending on the specific disaster context, available resources, and epidemiological situation.

Mass vaccination campaigns 🔗

Mass vaccination involves immunising entire populations within a defined geographic area, regardless of individual risk factors or prior vaccination status. This approach aims to rapidly achieve high coverage levels to establish herd immunity and prevent outbreaks before they begin. Mass vaccination centres are typically set up in non-healthcare locations like schools, stadiums, or community centres to accommodate high volumes of people efficiently.

During the acute phase of emergencies, mass measles vaccination campaigns are standard practice. Current guidance recommends swift preventive vaccination including all children from 6 months through 14 years of age, along with vitamin A supplementation. Studies of measles vaccination in humanitarian emergencies show that campaign-based responses are predominant in these settings, often done in coordination with UN agencies and disaster relief organisations.

Mass campaigns require substantial resources: adequate vaccine supplies, cold chain infrastructure to maintain proper storage temperatures, trained personnel, and robust logistics networks. The challenge intensifies in post-disaster scenarios where transportation routes may be damaged, healthcare facilities destroyed, and power supplies unreliable.

Targeted vaccination approaches 🔗

Targeted vaccination focuses immunisation efforts on specific high-risk populations or geographic areas rather than entire communities. This approach conserves limited vaccine supplies while directing resources toward those most likely to benefit. Targeting criteria might include age groups, occupational exposure, health status, or residence in areas with confirmed disease transmission.

Following Cyclone Tomas in Fiji in 2010, health authorities conducted an emergency typhoid vaccination campaign targeting cyclone-affected areas as part of the post-disaster response. Impact evaluations demonstrated reduced disease burden in areas where a large proportion of the population received vaccines compared with unvaccinated areas-validating the effectiveness of geographically targeted approaches.

Ring vaccination represents a specific targeted strategy where contacts and contacts of contacts surrounding confirmed cases receive priority vaccination. This approach proved highly effective during the 2014-2016 Ebola outbreak in West Africa, demonstrating the value of precisely targeted interventions when appropriate vaccines and surveillance capacity exist.

Challenges in post-disaster vaccination 🔗

Implementing vaccination programmes after disasters presents numerous obstacles. Cold chain disruption ranks among the most significant challenges-many vaccines require refrigeration at 2-8°C, and some newer vaccines need ultra-cold storage at -60°C or below. When power infrastructure fails and transportation routes become impassable, maintaining vaccine potency becomes extraordinarily difficult.

Security concerns in conflict-affected areas can dramatically limit access to populations in need. Targeted attacks on health workers during polio eradication efforts in some regions illustrate how insecurity can undermine vaccination campaigns. Curfews and access constraints limit staff movement and delay operations. Additional costs for charter flights and enhanced security measures increase programme expenses substantially.

Supply shortages frequently constrain emergency responses. When multiple emergencies occur simultaneously, global vaccine stockpiles may be insufficient to meet demand. During yellow fever outbreaks in Angola and the Democratic Republic of Congo in 2016, the global stockpile had to be replenished multiple times, and authorities ultimately implemented fractional dosing strategies to extend limited supplies.

Accurate population data is often unavailable following disasters. Displacement makes it difficult to estimate target population sizes or track who has received vaccines. Community trust and vaccine acceptance may be compromised if rumours or misinformation circulate, particularly in contexts where populations are already traumatised and distrustful of authorities.

Vaccination guidelines by WHO and PAHO 🔗

International health organisations have developed comprehensive frameworks to guide vaccination decisions during emergencies. These guidelines help authorities make evidence-based choices about when, what, and how to vaccinate in challenging circumstances.

WHO decision-making framework 🔗

The WHO framework for vaccination in acute humanitarian emergencies provides a transparent, rigorous methodology for deciding on vaccination options. It consists of three essential steps that responders must systematically evaluate.

Step one involves assessing local epidemiological risks of vaccine-preventable diseases among the affected population. This includes examining pre-emergency vaccination coverage, disease incidence patterns, and factors that might increase transmission such as overcrowding, malnutrition, and compromised water and sanitation.

Step two focuses on vaccine selection and characteristics. Responders must consider vaccine availability, storage requirements, dosing schedules, contraindications, and expected effectiveness in the specific population. Some vaccines require multiple doses administered weeks apart, which poses logistical challenges in unstable emergency settings.

Step three examines local contextual constraints that affect implementation feasibility. This includes assessing healthcare workforce capacity, supply chain functionality, security conditions, community acceptance, and available financial resources. The framework emphasises that vaccination should result in net benefit-saving lives and reducing disease burden while not diverting resources from other critical interventions.

Key factors influencing vaccination strategy 🔗

Population susceptibility is a primary consideration. Areas with historically low vaccination coverage or immunocompromised populations require more aggressive intervention. Pre-emergency epidemiological data, when available, helps identify immunity gaps.

Accessibility determines whether populations can be reached with vaccination services. Remote areas, active conflict zones, and regions with damaged infrastructure may require mobile teams, door-to-door campaigns, or coordination with military or humanitarian actors to achieve access.

Vaccine availability constrains all planning. The Humanitarian Mechanism developed by WHO, UNICEF, Médecins Sans Frontières, and Save the Children enables organisations to quickly procure affordable vaccine supplies for populations facing emergencies. This mechanism has been available since 2017 to address supply challenges.

PAHO regional guidance 🔗

The Pan American Health Organization provides regional coordination for emergency health responses in the Americas. PAHO supports Member States in assessing post-disaster health situations and potential risks to public health, including vaccine-preventable disease threats.

PAHO’s emergency response emphasises integration of vaccination within broader health system recovery efforts. Rather than treating vaccination as an isolated intervention, the organisation promotes embedding immunisation services within primary healthcare restoration and comprehensive disease surveillance. This approach ensures sustainability beyond the acute emergency phase and builds long-term health system resilience.

Recent PAHO initiatives demonstrate practical application of these principles. During Haiti’s ongoing humanitarian crisis, PAHO coordinated emergency shipments including vaccines while simultaneously working to strengthen routine immunisation capacity despite extremely limited health facility functionality.

Looking ahead: building preparedness 🔗

The ultimate goal extends beyond emergency response to preparedness and prevention. Maintaining high routine vaccination coverage reduces vulnerability when disasters occur. Strong health systems with reliable cold chains, trained personnel, and robust surveillance can pivot more quickly to emergency modes. Pre-positioned vaccine stockpiles and established coordination mechanisms accelerate response when crises emerge.

Climate change is increasing the frequency and severity of disasters while simultaneously shifting disease patterns. New populations are becoming exposed to vector-borne diseases, and flooding events spread waterborne infections like cholera. This evolving landscape demands adaptive immunisation strategies that anticipate emerging threats.

What do you think? Given the increasing frequency of climate-related disasters, how should communities and health systems prioritise vaccination preparedness in their disaster planning? What role should local health workers play in ensuring immunisation continues during emergencies?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC4685677/
2. https://www.who.int/teams/immunization-vaccines-and-biologicals/essential-programme-on-immunization/implementation/vaccination-in-humanitarian-emergencies
3. https://www.immunizationagenda2030.org/strategic-priorities/outbreaks-emergencies
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC8230199/
5. https://ncbi.nlm.nih.gov/pmc/articles/PMC3195113
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC5711321/
7. https://www.who.int/publications/i/item/WHO-IVB-17.03
8. https://www.who.int/publications/m/item/the-humanitarian-mechanism
9. https://www.paho.org/en/topics/health-emergencies-and-disaster-response