Climate strategies must take vaccination into account
Climate-driven shifts in temperature, precipitation and nutrient availability are altering the transmission and distribution of human, animal and plant pathogens. More than half of all infectious diseases that affect humans are aggravated by climate change, with low- and middle-income countries (LMICs) bearing a ten-times-higher burden of infectious diseases than their affluent counterparts. Despite contributing little to its causes, LMICs are disproportionately vulnerable to the consequences of climate change, as they are situated in the world’s warmest regions, are heavily reliant on natural resources and have limited capacity to handle climate extremes. These vulnerabilities, compounded by inequalities linked to gender, ethnicity and income, converge into a ‘perfect storm’ of climate-driven infectious disease challenges; another reminder that the climate crisis is a health crisis. Rising temperatures and extreme weather events disrupt vaccine distribution, weaken health systems and displace populations, increasing the susceptibility of vulnerable communities to infectious disease outbreaks. This complicates the task of ensuring the consistent and equitable delivery of vaccines. In countries facing conflict and humanitarian crises, vaccination rates across both humans and livestock are often alarmingly low.
Approximately one-fifth of zero-dose children, defined as those who have not received any routine vaccines, live in conflict settings. In the face of these challenges, there is an urgent need to both safeguard and amplify the potential of vaccines to counteract the influence of climate change on infectious diseases. Recognizing that the well-being of animals, humans and the environment are intrinsically linked, we suggest a One Health approach that prioritizes multi-disciplinary collaboration in vaccine and climate research, advocates for the monitoring and forecasting of climate-induced disease impacts, and, finally, offers a pathway towards optimized vaccine delivery systems.
Bridging vaccines and climate research and development
We identify five key global research and development (R&D) priorities for enhancing vaccines as a tool for climate resilience.
Firstly, while we know that climate change will exacerbate infectious diseases, there is a critical gap in our understanding of the extent, direction and intensity of this impact. The following examples are areas where the impacts of climate change are predicted to be particularly pronounced, but where the full scope of these impacts remains uncertain. Water-borne diseases such as cholera increase in incidence with extreme temperatures and precipitation, through water and food contamination from poor water, sanitation and hygiene (WASH) infrastructure. Temperature and precipitation changes influence the prevalence of vector-borne diseases such as malaria, dengue, yellow fever and Zika. Small island states and coastal communities face particular climate vulnerabilities through rising sea levels, tropical cyclones and flooding, increasing vector-borne and diarrhoeal diseases such as typhoid. Ecosystem disruptions also alter disease vector distribution and behaviour, increasing spillover risks and outbreaks such as Ebola, Marburg and Nipah, and the threat of pandemics as seen with COVID-19. To establish robust early warning forecasting systems, we must bridge the knowledge gap on how climate change will impact the burden of infectious diseases, and strengthen the evidence base from underrepresented LMICs.
Secondly, there is a shortage of vaccines for emerging pathogens and diseases of epidemic concern that are driven directly and indirectly by climate change. The R&D Blueprint of the World Health Organization (WHO) identifies high-risk diseases and pathogens that pose epidemic potential, many of which still lack vaccines, such as Marburg virus disease, Nipah and Zika. Key to continued success will be a transdisciplinary ‘One Health vaccinology’ approach that leverages scientific synergies between the human and veterinary sectors to address shared climate-related infectious disease threats, with the added benefit of resource efficiency. Fourth, implementation research with communities directly impacted by climate change is essential to guide vaccine introduction and scale-up, especially among marginalized populations. Implementation science offers an effective means to address barriers and bottlenecks that affect vaccination programmes. The lessons from the COVID-19 pandemic underscore the importance of this, as vaccine hesitancy and resistance to life-saving vaccines compromised uptake, even in high-income countries.
Lastly, R&D must come from the contexts where the climate and health impacts are being felt, requiring a critical mass of researchers and climate and health leaders in LMICs. Fostering homegrown solutions and intellectual capital requires long-term vision, funding, R&D infrastructure and supportive environments.
Monitoring and forecasting climate’s disease impact
Decision-makers, at both the global and local levels, are increasingly confronted with the task of preparing for climate-sensitive disease shifts and outbreaks. A notable gap seen with the new climate indicator has been the lack of essential integrated climate and infectious disease data. To address this, we need strengthened infectious disease surveillance across both the human and animal sectors, integrated with climate-sensitive forecasting systems in LMICs. These systems are vital for early detection and the planning of infection control and vaccination responses to climate-related infectious disease outbreaks. Despite the urgent need, integrating climate and environmental science data with disease epidemiology and ecology data has not yet been broadly adopted in public-health practice as challenges remain in harmonizing climate and health data. Strengthening surveillance and forecasting capabilities in LMICs will also allow for targeted community engagement activities, such as education campaigns and support for vaccine acceptance, and for the implementation of vector control measures for more proactive and effective climate-influenced outbreak management.
Strengthening vaccine last-mile preparedness and delivery
A vaccine cannot deliver on its potential unless it reaches those who need it, when they need it. To strengthen climate-responsive vaccine delivery, the entire supply chain from manufacturing to distribution must demonstrate adaptability and resilience to climate disruptions. The COVID-19 pandemic has exposed vaccine nationalism tendencies as countries prioritized their populations, reducing access for countries in need and further exacerbating global health disparities. To counteract this, we must expand and diversify sustainable vaccine manufacturing capacity in LMICs.
Vaccine delivery chains must also be capable of withstanding extreme climates with limited infrastructure. Finally, establishing emergency vaccine stockpiles for climate-sensitive diseases and optimizing their utilization during sudden surges in demand are essential to strengthen the climate resilience of vaccine supply.