Impact of climate change on vaccine responses and inequity

Abstract

Climate change poses a substantial threat to global health by altering environmental conditions and impacting vaccine effectiveness. We explore how climate change impacts vaccines and worsens inequities, highlighting the need for further research and targeted interventions.

Climate change has evolved into a multidimensional challenge affecting various facets of human health. In the absence of climate mitigation, 3.5 billion people are projected to be exposed to a mean annual temperature ≥29.0 °C in the next 50 years¹. Climate change-related trends and events (for example, extreme heat and cold, floods) pose substantial direct and indirect health risks globally, including increased morbidity and mortality rates². Furthermore, climate change has shifted the geographical distribution of certain insect vectors and environmental conditions, bringing infectious diseases to new areas. While addressing the many health effects of climate change will require complex mitigation and adaptation strategies, some negative outcomes may be vaccine-preventable, and improving vaccine access and uptake could help to reduce some of these challenges. However, emerging evidence demonstrates the profound impacts that climate change can have on vaccine efficacy, safety and access (Fig. 1). We discuss these concerns and highlight potential future strategies for optimizing vaccine development, storage, transportation and equitable access, ensuring efficacy and resilience in a changing climate.

Fig. 1 |. Impact of climate change on vaccine efficacy, safety and inequity.

Climate change-related factors, including extreme temperature (heat/cold), humidity, flooding and droughts, can cause pathogen variation, compromise vaccine storage and transportation, and affect immune responses. These factors compromise vaccine efficacy and safety, particularly in marginalized populations, and impact vaccine stability and host responses, leading to negative health outcomes. As a result, climate change can suppress positive immune responses to vaccines and increase adverse events to vaccines, further exacerbating vaccine inequality.

Impacts on effectiveness, storage and transportation

Climate change can alter the geographic spread of pathogens³, but altered climate regimes such as global warming and climate change may induce selection pressure on pathogens and pathogen spillover, increasing virulence and potentially even leading to the emergence of new pathogen variants that may evade existing vaccines⁴. Climate-related factors can compromise immune function — for example, heatwaves could weaken the adaptive immune response to influenza infection in a laboratory mouse model⁵ — which may also lead to reduced responses to vaccination. Marked differences were observed in host antibody response to the poliovirus vaccine between seasons, with responses more robust in winter than in summer⁶, further supporting the role of climate factors in vaccine responses.

Climate changes may also cause physical or functional damage to vaccines due to compromised storage and transportation, reducing stability, lifespan and effectiveness. High temperatures can denature vaccine proteins, rendering them less effective or even inactive, while extremely low temperatures may alter the structure of vaccine components, impacting their ability to provoke the desired immune responses⁷. Vaccine efficacy is thermally labile to temperature changes, with most vaccines requiring a cold chain of 2–8 °C to prevent degradation⁷. Both heat and freezing temperatures can damage many vaccines, including diphtheria, tetanus and acellular pertussis (DTaP) and hepatitis B vaccines^5,7. A changing climate increases the risk of temperature fluctuations during transportation and storage, and elevated temperatures accelerate the degradation of vaccine ingredients, reducing potency and efficacy, which is particularly concerning in regions experiencing extreme temperatures⁸. Changes in precipitation and humidity can also deteriorate vaccine formulations by causing moisture ingress or evaporation, affecting the overall stability of vaccines and potentially diminishing their shelf life.

Impacts on safety

Climate change has multifaceted implications for vaccine safety, impacting both the stability of the vaccines themselves and host responses to vaccines. The negative impact of climate change on vaccine safety is manifested explicitly in the adverse events of vaccines⁹. Our analysis of the Vaccine Adverse Event Reporting System reports between 13 December 2020 and 28 December 2022 revealed noteworthy patterns in adverse events reported during different seasons¹⁰. Previous studies^9,10 showed that during the warmer spring–summer months, individuals might be more prone to conditions such as heat-related symptoms (pyrexia) and dehydration, which could contribute to reported adverse events such as dizziness and fatigue. By contrast, the autumn–winter season sees an increased prevalence of respiratory infections and exacerbating symptoms such as muscle pain (myalgia). The distinct seasonal profile of adverse events may be influenced by climate-related variations. Changes in temperature, humidity and other environmental factors can affect the prevalence and severity of certain health conditions, potentially increasing adverse events. Beyond these direct impacts, if adverse events are perceived as more frequent or severe due to climate factors, people may become less willing to receive vaccinations, which could negatively affect public health.

Impacts on inequity

Climate change exacerbates vaccine inequity indirectly by disrupting health systems and services, including vaccination programmes, impeding vaccine distribution and altering climate-related infectious disease patterns. As a result of a changing climate, the likelihood, frequency and severity of extreme weather events are increasing, which necessitates better preparation in healthcare systems¹¹. Events such as heatwaves, hurricanes and floods present numerous challenges to health systems (for example, affecting operations, damaging facilities, and impacting healthcare professionals and patients)¹¹. These impacts extend to vaccine services and probably result in behaviour and outcome changes, making it more challenging to provide access to marginalized populations.

Extreme weather events are projected to occur more frequently and with greater severity, necessitating preparation and adaptive actions to mitigate their impacts. In 2019, Cyclone Idai caused severe flooding in Mozambique that led to a cholera outbreak due to contaminated water sources¹², which illustrates both the challenges and the importance of preparedness. The Mozambican Ministry of Health quickly launched a cholera vaccination campaign, reaching more than 800,000 people and achieving high uptake with positive public perception¹². However, this campaign also highlighted challenges, such as the destruction of infrastructure and the logistical difficulties of vaccinating large, mobile populations, particularly in low-income or remote areas¹².

Climate change influences the geographic distribution, spread and burden of vaccine-preventable infectious diseases through changes in temperature, precipitation and rainfall patterns¹³. For example, the IPCC Sixth Assessment Report predicts that the distribution and seasonal transmission of vector-borne diseases will increase in Africa, potentially exposing tens of millions more people¹⁴. As a result, climate change is causing shifts in disease prevalence in specific regions and worsening susceptibility, particularly in marginalized populations. These complexities contribute to challenges in achieving equitable vaccine distribution.

Actions for vaccine security under climate change

To address these challenges, we propose the following actionable recommendations for decision-makers. (1) Building resilient vaccine infrastructure in climate-vulnerable regions, including distribution and production. This includes establishing more robust cold chain systems and mobile vaccination units to reach remote areas. (2) Better understanding molecular mechanisms of how climate change factors affect vaccine effectiveness and safety. (3) Identifying marginalized populations and implementing strategies to ensure equitable access to vaccines, as these groups are often disproportionately affected by disasters and have limited access to healthcare facilities. Community engagement and targeted outreach programmes can improve vaccine coverage in these populations. And (4) integrating vaccines into emergency preparedness and response plans, including strategies for rapid deployment during crises and communication strategies to enhance vaccine literacy. This effort should involve creating adaptable vaccination campaigns that can be mobilized quickly in response to extreme weather events, ensuring the continuity of vaccination efforts during emergencies.

Conclusion

Vaccination has been proposed as a strategy to mitigate the effects of climate change on human health^13,15, yet the negative impacts of climate change on vaccination must also be considered. We emphasize the pressing need to understand how climate change affects vaccine responses, including efficacy, safety and equity. While it is known that climate change affects infectious diseases, its specific impacts on vaccine-induced immunity and inequality remain largely unknown. Addressing these critical questions is essential, as reduced vaccine efficacy in extreme environmental conditions can undermine efforts to protect vulnerable populations from preventable illnesses. Continued monitoring and analysis of vaccine response and adverse event data concerning climatic changes will enhance our understanding of vaccine safety, ultimately informing public-health strategies and interventions. Prioritizing research in this area is vital to ensure the effectiveness of vaccination programmes, especially for those most vulnerable to the changing climate.