For decades, immunization has served as one of the most effective public health strategies to reduce morbidity and mortality from infectious diseases. According to Carter et al. [1] , vaccination is expected to prevent about 4.4 million deaths annually between 2021 and 2030 by protecting against 14 vaccine-preventable diseases across 194 countries. Similarly, Shattock et al. [2] in their historical analyses showed that since the launch of the Expanded Program on Immunization in 1974, global vaccination efforts have saved approximately 154 million lives, 146 million of them among children under age five, including over 100 million infants. These big wins represent more than 10 billion years of healthy life added, with each prevented death contributing, on average, 66 years of full health. As of 2024, children under 10 are 40% more likely to survive to their next birthday compared to a world without historical vaccination efforts, with benefits extending well into adulthood [2] .

In the United States, vaccines have made a remarkable difference in the health of families and communities at large. This became even more evident following a measles resurgence in the early 1990s, which led to the creation of the Vaccines for Children (VFC) program in 1994 to ensure that eligible children could receive free vaccines, regardless of their families’ ability to pay [3] . Since then, routine childhood immunizations have prevented an estimated 508 million illnesses, 32 million hospitalizations, and over 1.1 million deaths among children born between 1994 and 2023 [4] . Economically, this translated into USD 780 billion in direct medical savings and USD 2.9 trillion in societal cost savings. Even after factoring in the costs of vaccination programs, the net savings stood at USD 540 billion (payer perspective) and USD 2.7 trillion (societal perspective), with benefit-cost ratios of 3.3 and 10.9, respectively [4] . This presents clear, strong evidence that immunization not only saves lives but also delivers a high return on investment.

Prior to the introduction of the measles vaccine in 1963, Illinois experienced substantial morbidity and mortality consistent with national trends. In the United States at that time, measles annually resulted in approximately 500 deaths, 48,000 hospitalizations, and 1000 cases of brain swelling. However, following widespread vaccine implementation, measles incidence sharply declined, and for decades the disease was effectively eliminated as a major public health threat in Illinois, though isolated outbreaks have emerged in recent years [5] - [7] . Building upon decades of immunization successes, and in recognition of the continued need for high coverage, Illinois has maintained strong immunization programs, most notably through active participation in the federal VFC program. This initiative provides, at no cost, the ACIP-recommended vaccines to Medicaid-eligible, uninsured, and underinsured children under 19 years of age across Illinois. As evidence of its impact, more than 70% of Illinois schools report measles, mumps, rubella (MMR) vaccination coverage above 95%, and statewide rates remain consistently above the threshold needed for herd immunity [8] .

These achievements, however, rely not only on scientific advances in vaccine development to keep vaccines potent and effective, but also on the day-to-day efforts of the people and systems responsible for storing, transporting, and administering vaccines, i.e., maintaining the vaccine cold chain up to the point of administration, systems that communities around the world count on to stay safe. Yet these systems remain vulnerable, especially in the face of severe weather events, which may cause storage-unit failures leading to temperature excursions - instances when vaccines are exposed to conditions outside the recommended temperature range [9] , as well as shipping delays, all of which can compromise vaccine viability, pose serious risks to public health, and lead to significant vaccine wastage and financial losses. It is important to note that these losses are felt at multiple levels. For instance, publicly funded immunization programs may absorb the cost of replacing federally purchased vaccines; private healthcare providers may incur unrecoverable losses when weather events compromise their private vaccine stock; and manufacturers and distributors can experience operational and financial strain from disrupted delivery chains. Ultimately, the burden extends to the government, which must allocate budgetary funding and manage broader public health consequences.

Illinois, situated in the U.S. Midwest region, has experienced significant changes in weather patterns over the past century. For instance, the state’s average temperature has increased by approximately 1 - 2˚F since the early 1900s, accompanied by greater variability in winter storm patterns [10] . Similarly, Hayhoe et al. [11] noted that the Midwest, Illinois inclusive, is warming at about 0.4˚F per decade and is experiencing a doubling in the frequency of heavy rainfall events, alongside increasingly intense heatwaves and altered snow and ice patterns. Moreover, the U.S. Environmental Protection Agency [12] reports a 10 - 20% increase in overall annual precipitation in Illinois, a 35% rise in heavy-precipitation events, more frequent flooding, and prolonged periods of extreme summer heat. These significant changes in weather patterns and accompanying weather-related events ultimately heighten the risk of disrupting vaccine storage and transport systems.

While Illinois’ immunization successes are often discussed through the lens of the federally funded VFC program, a substantial share of routine vaccination doses are also privately purchased and stored by providers in Illinois. Although Food and Drug Administration (FDA) regulations define vaccine storage and stability requirements through product labeling, CDC guidance provides the operational framework for vaccine storage, handling, and incident management, particularly within federally funded programs [9] . Under this CDC framework, vaccine incident reporting and replacement procedures are most clearly detailed for publicly purchased vaccines (e.g., VFC/317) within CDC and Illinois VFC guidance [9] [13] . In contrast, for privately purchased vaccines, incident reporting typically follows the manufacturer’s directions, which reflect FDA-approved stability information, and/or payer or facility policy. Publicly available sources reviewed for this paper do not indicate that vaccine incidents involving privately purchased vaccines by providers in Illinois are routinely reported through the Illinois VFC program, although reporting practices may vary by jurisdiction [9] [13] . Across all public sources reviewed for this paper, we did not identify Illinois-level, cause-coded, statewide aggregates that include both publicly funded and privately purchased doses affected by weather-related temperature excursions or shipping delays, leaving the public scale of impact across the state’s entire vaccine supply system unclear.

This scoping review aims to explore how severe weather events disrupt the vaccine cold chain in the U.S., with a focus on Illinois, and to integrate publicly available evidence on their impact on vaccine storage, shipping, and program sustainability. Given the increasing frequency of weather-related disruptions, strengthening vaccine cold-chain resilience is also integral to broader public health emergency preparedness and response (PHEPR) efforts, as maintaining vaccine viability and continuity of immunization services during disruptions directly supports emergency readiness and health system resilience [9] [13] [14] .

The preservation of vaccine integrity in the United States does not end at scientific development or clinical approval, but equally on a well-coordinated system that ensures vaccines developed for human use are consistently stored and transported under controlled temperature conditions known as the vaccine cold chain. This system is essential to preserving vaccine potency and safety from the moment of manufacturing until administration at the provider level [9] [15] . In essence, the cold chain is a system of temperature-controlled environments that preserves vaccine efficacy from manufacture through administration [9] [16] [17] . Thus, a disruption in the vaccine cold chain, even for a transient period, can lead to unsuitable conditions that irreversibly reduce vaccine potency, diminish immune responses, and increase the need for revaccination [9] . When such failure occurs, especially in cases where no manufacturer stability data support continued usage of vaccines, it can compromise public health, waste resources, and impose significant economic costs, including the price of discarded vaccines [18] , increased healthcare provider workload due to logistical challenges, resupply needs, documentation and reporting, inventory reconciliation, and efforts to investigate and correct storage and handling errors. These burdens also affect patient flow and access, leading to increased demands on human resources [9] [19] , and may contribute to erosion of public trust in immunization programs, particularly in an era marked by vaccine hesitancy. Beyond direct losses, cold-chain breaches create broader societal and economic burdens, such as the treatment of preventable diseases and reduced vaccination uptake [20] .

These risks often manifest as temperature excursions (TEs), which are instances where vaccines are exposed to conditions outside the recommended temperature range [9] . Whether these deviations involve excessive heat or freezing temperatures, they signal a breach in cold-chain integrity [9] . While TEs may occur from various causes, this review focuses specifically on weather-related disruptions, especially their role in contributing to storage-unit failures and shipping delays within the context of Illinois. Given the well-established shifts in Illinois’ climate, including more frequent extreme heat events, heavier precipitation, and seasonal storms, these evolving weather patterns are especially relevant to understanding vaccine cold-chain vulnerabilities. Rather than hypothetical, these concerns are grounded in observable patterns across the Midwest, where temperature variability and the intensity of weather events have increased significantly over recent decades [11] [12] . These increasingly unpredictable events are especially concerning for cold-chain systems that rely on stable power and timely distribution. Beyond definitions, U.S. clinic data underscore how often storage units drift out of range in practice: in a county outpatient system study of 54 refrigerator compartments, 26 (48%) stayed within the WHO-recommended 2 - 8˚C range, 13 (24%) recorded at least one freezing episode, 10 (19%) ran just above freezing at 0.1 - 1.9˚C without freezing, and 5 exceeded 8˚C during the observation period, as captured by graphic-output data loggers [21] . To contextualize exposure to severe events in Illinois, this review references National Oceanic and Atmospheric Administration’s (NOAA’s) Storm Events Database (1950-present, county-level records), which is used later to summarize event frequency [22] .

Power outages, especially those linked to heatwaves or severe storms, pose a serious risk to vaccine storage. Although pharmaceutical-grade refrigerators are preferred for their superior temperature stability under normal conditions, their performance during electrical outages is notably poor. A National Institute of Standards and Technology (NIST) report found that pharmaceutical units, especially those with glass doors, reached the critical 8˚C threshold in just 45 to 140 minutes following a power loss, with vaccines likely rendered unusable within one to two hours [23] . These short time-to-warm intervals are exactly why CDC emphasizes continuous digital monitoring. Consistent with that guidance, NIST’s multi-model evaluations of digital data loggers showed devices maintained accuracy across 0 - 10˚C and remained stable over many months of operation, and the studies detail practical probe-in-glycol setups and ice-point checks that reflect liquid vaccine temperatures in routine clinics [24] .

This window is especially concerning when compared to average power outages in the U.S., which occur about 1.5 times annually and last about 3.5 hours, more than enough time for cold-chain failure to occur [25] . These realities demonstrate the vulnerability of vaccine storage units during common grid interruptions. Furthermore, severe storms and flash floods may disrupt transportation routes, delay vaccine shipments, or make last-mile delivery unsafe, increasing the risk of TEs during transit. For example, Winter Storm Uri in February 2021 caused widespread logistical breakdowns (power outages, road closures, and delivery disruptions), which delayed COVID-19 vaccine distribution across multiple states. The White House later reported that nearly six million doses were delayed due to winter weather nationwide, with courier systems and over 2000 vaccination sites affected by hazardous conditions and power failures [26] . White House briefings that week likewise cited approximately six million doses delayed, about three days’ shipments, affecting all 50 states [27] . In Illinois specifically, state officials confirmed that adverse weather disrupted federal vaccine shipments in mid-February 2021, prompting the Illinois Department of Public Health to proactively draw from strategic stock to maintain vaccination operations until delayed deliveries resumed [28] .

Across the United States, the electric grid continues to demonstrate vulnerabilities due to severe weather, with impacts particularly evident in the Midwest. Over the years, severe weather events such as derechos, tornadoes, and blizzards have increasingly disrupted power systems, causing significant risks to public-health infrastructure, including vaccine cold-chain integrity. According to utility-submitted data compiled by the U.S. Energy Information Administration (EIA), the average annual outage duration for customers in the United States exceeds 200 minutes (approximately 3.3 hours) when major events are included [29] . These durations can easily exceed the warm-up windows of common pharmaceutical units during an outage, emphasizing the need for automated and reliable backup systems. As previously noted, even brief lapses in power can produce conditions that compromise vaccine efficacy. This reinforces the urgency of infrastructure resilience and targeted planning, particularly in healthcare settings that rely on uninterrupted vaccine cold-chain storage. Meanwhile, Illinois has experienced persistent, and at times acute weather-related disruption to electrical service. For example, publicly reported local utility data have described severe thunderstorms in Champaign County, causing outages for over 1800 customers in a single event, highlighting recurring vulnerability even during non-catastrophic weather.

More comprehensively, the EAGLE-I database, a publicly available, benchmark county-level dataset with 15-minute outage resolution covering 2014-2022, shows that Illinois counties regularly face outages nearly on a weekly basis, even in the absence of declared major events [30] [31] . These localized and transient outages, often small in scale, may not significantly influence statewide averages but nonetheless pose risks to vaccine storage units, which require uninterrupted power to maintain cold-chain temperatures. To document the data source and coverage details, we reference public EAGLE-I releases (2014-2022; 15-minute resolution) available via Oak Ridge National Laboratory (ORNL) and Office of Scientific and Technical Information (OSTI) [31] . In contrast, utility-level reliability metrics paint a more favorable picture. In 2022, Commonwealth Edison (ComEd) reported a System Average Interruption Duration Index (SAIDI) of 29 minutes and a System Average Interruption Frequency Index (SAIFI) of 0.43, placing ComEd among the top-performing utilities nationwide in terms of overall reliability [32] . However, such aggregate indicators can obscure the frequency and impact of smaller, localized outages that still threaten sensitive operations like vaccine cold-chain storage. Further highlighting this vulnerability, the VA Office of Inspector General reported that on May 4, 2023, the Edward Hines Jr. VA Hospital’s IT Center endured a 22-hour outage, evidence that even critical healthcare infrastructure around Chicago remains susceptible to extended power loss [33] . Taken together, these data sources emphasize that power outages in Illinois are both frequent and consequential, reinforcing the urgent need for robust backup planning and real-time monitoring in vaccine cold-chain systems.

While there is widespread acknowledgment of how critical the vaccine cold chain is to preserving vaccine potency and ensuring immunization safety, there remains little to no publicly available data quantifying vaccine losses, especially those stemming from weather-related disruptions across most U.S. jurisdictions, including Illinois. In accordance with current CDC guidance, VFC providers are expected to follow a structured response protocol after any suspected temperature excursion. This includes isolating the affected vaccines, downloading and reviewing temperature data, and contacting the manufacturer to assess vaccine viability [9] [13] . In the meantime, vaccines must not be discarded or administered until providers receive further instructions from their respective immunization programs. In Illinois, the IDPH VFC Provider Manual offers similar steps, including submitting a detailed vaccine incident report and the manufacturer’s vaccine stability statement to the immunization program for review [13] . The vaccines involved in the temperature excursion are marked “Do Not Use” until the state’s immunization program confirms whether they can be safely used or must be wasted and/or replaced [13] . These standard protocols not only help ensure timely and coordinated responses to temperature excursions and uphold vaccine safety and accountability, but also demonstrate how vaccine cold-chain incidents are typically resolved at the provider-jurisdiction level.

What remains far less clear is how the data from these incidents are used once the immediate issue has been resolved, an important gap, given that understanding how vaccine cold-chain failures occur, and how frequently, is essential for informing broader systems-level improvements, especially in the context of increasing weather-related disruptions [9] [17] [18] . Yet despite this need, at the time of this writing, there is no centralized or public-facing data showing the number, causes, or trends of vaccine cold-chain incidents reported across jurisdictions in the United States. It is not clear whether states like Illinois systematically report these incidents to the CDC or whether they are aggregated in any meaningful way for national or state-level review. More importantly, while individual vaccine temperature excursions may be documented at the provider or jurisdiction level, there is no publicly accessible or centralized data at either the state or federal level, that show how many cold-chain failures were weather-related, how often shipping delays resulted in temperature excursions, or how many doses were affected. The absence of such a database creates a visibility gap that may limit understanding of the broader impact of weather-related disruptions on vaccine viability and could constrain the ability of public health agencies, researchers, and system planners to identify trends in weather-related cold-chain failures, strengthen preparedness strategies for storage-unit risks and shipping delays, and build long-term resilience in vaccine distribution systems, especially as climate patterns continue to shift across Illinois and the broader United States. To situate weather- and power-related risks within officially declared events, we also reference OpenFEMA’s Disaster Declarations Summaries for Illinois (2000-2025) [14] .

Even when such incidents are resolved at the state level and vaccine losses are absorbed without disrupting service delivery at the provider level, the absence of publicly accessible and aggregated reporting may limit broader system-level understanding. While internal reporting structures may exist in the Illinois VFC program, the lack of publicly shared data makes it difficult for jurisdictions and stakeholders to compare risks, identify trends, and coordinate long-term climate-resilience strategies. Without that visibility, they may be less equipped to anticipate risk hotspots and implement climate-resilient responses, such as planning for mobile-refrigeration deployment, assisting with shipment-issue resolution, or providing technical support to high-risk areas. While jurisdictions do not manage shipping routes directly, aggregated data on cold-chain disruptions could also help inform logistics partners in refining delivery strategies for vulnerable areas. In this context, the issue is not only whether providers report excursions, but how those reports are aggregated, analyzed, and applied, or not applied, to inform broader strategies that strengthen the vaccine cold chain in a changing climate, including in Illinois, where these risks are becoming increasingly relevant. Thus, as climate-related risks continue to increase, public health programs cannot afford to treat vaccine cold-chain failures as isolated, one-time events. Each failure is a missed opportunity to learn and strengthen the system. Providers are already required to report temperature excursions to their jurisdiction’s immunization program, regardless of the cause, and the Illinois VFC program has established protocols for reviewing these incidents, including submission of vaccine-incident reports and manufacturer stability documentation [9] [13] . However, what remains unclear is whether these jurisdiction-level reports are shared with CDC in a systematic way, or if any national database aggregates, analyzes, or makes this information publicly available. To date, there is no centralized platform where the frequency, causes, or outcomes of reported excursions, especially those tied to weather-related disruptions, can be reviewed across jurisdictions. This absence of visibility makes it difficult to identify patterns, learn from previous events, or inform larger strategies for vaccine cold-chain resilience in the face of worsening and evolving climate threats. This scoping review addresses that gap by examining what is currently known, what patterns are emerging, and what practical strategies or technologies could help prevent future disruptions, particularly in Illinois, where weather-related risks to vaccine storage and delivery are becoming more common and more consequential [11] [12] .

One practical area of opportunity lies in the use of smart cold-chain technologies, especially AI-enabled data loggers that are now capable of monitoring vaccine storage conditions in real time. Unlike traditional data-logger models that require providers to download and review temperature logs manually each week, these newer systems automatically upload readings to secure cloud platforms, analyze them continuously, and send alerts when a temperature excursion is either occurring or imminent [34] . Additionally, many platforms now integrate wireless IoT sensors and GPS-enabled trackers, allowing real-time monitoring of both temperature and shipment location throughout the cold chain. Automated alerts are triggered the moment any deviation occurs, and cloud-based dashboards ensure that providers or program staff can access data remotely from anywhere. While providers ultimately retain responsibility for vaccine storage compliance, these systems ease daily monitoring demands, reduce the risk of missed excursions, and offer earlier detection of potential failures [34] . Some systems, such as PharmaWatch™, go further by reducing dependence on local Wi-Fi or internal IT infrastructure. Using cellular, multi-carrier connectivity and battery-backed transmission, these tools can support real-time monitoring even during power or internet outages, which is especially valuable for rural or low-resource clinics where traditional connectivity may be unreliable [35] . These solutions reflect broader trends in the vaccine supply-chain space, where predictive and automated tools are increasingly used to support cold-chain stability and enable early intervention before a breach leads to vaccine loss [36] , a point also discussed in a peer-reviewed review of cold-chain temperature monitoring [37] . A more recent example is the development of “active prediction” systems such as MaxTrace, presented by MaxQ Research at the ISTA TempPack Forum. Unlike conventional monitoring tools that alert after an excursion begins, these systems are designed to detect patterns that indicate an excursion is about to occur, sending alerts in advance so providers can act before temperatures move out of range [36] . This kind of forward-facing innovation moves beyond real-time alerts and toward real-time prevention, which is exactly the direction public-health cold-chain systems need. Even more importantly, these systems should begin to integrate environmental data such as weather forecasts and regional power-outage modeling, especially as severe storms, heatwaves, and floods become more common causes of cold-chain disruption. While no publicly documented system yet combines weather-predictive alerts with storage-unit-specific risk assessment, this kind of integrated tool could be transformative. Imagine a platform that not only monitors storage temperature, but also receives advanced weather alerts, predicts power-grid instability, and automatically notifies the provider that a storage unit is at high risk of excursion within the next few hours, well before any temperature change actually begins. This level of integration would be especially beneficial to rural clinics, where backup power options may be limited and early action is critical to preventing vaccine loss. As the climate continues to change, this is the kind of thinking and design the public-health sector should prioritize, not as a luxury, but as a practical necessity for system-wide vaccine cold-chain resilience.

Overall, there is an urgent need to rethink how vaccine cold-chain risks are being managed in a changing climate. While providers and jurisdictions have established systems for responding to temperature excursions, there is limited visibility into how those incidents are tracked, shared, or applied to future planning. At the same time, smart technologies, including AI-enabled data loggers, predictive shipping tools, and proposed designs that could link weather forecasting with cold-chain risk alerts are showing what is possible when innovation is used to anticipate failure rather than react to it. For the immunization program in Illinois and beyond, the challenge is not just technical but structural: how do we bridge the gap between what exists, what’s emerging, and what is needed to build a vaccine cold-chain that is truly resilient to severe weather and power instability? This scoping review begins to address that question by mapping the current state of evidence in Illinois, identifying patterns in weather-related cold-chain disruptions, and exploring what practical strategies - technological, operational, and policy-based, can help protect vaccine integrity in the years ahead.

Severe weather and associated power outages pose persistent, well-documented risks to vaccine cold-chain integrity in the United States, including Illinois. Bench data show common pharmaceutical refrigerators can exceed 8˚C within ~45 - 140 minutes of power loss, while publicly reported power outages frequently extend beyond that window; Illinois also experienced weather-related shipping delays in February 2021. Within Illinois, strengths such as high MMR coverage and well-established vaccine incident reporting protocols sit alongside vulnerabilities in settings with less reliable power or backup capacity. Across the publicly accessible sources we reviewed, we did not identify cause-coded, statewide aggregated data linking weather/power exposures to dose-level outcomes (e.g., excursion counts, doses affected); this limits external visibility into patterns and equity, without speaking to internal analytic capacity.

Current guidance emphasizes continuous digital monitoring, connectivity-resilient reporting, and rapid procedures for moving vaccines to approved backup storage or redistribution. Vendor/trade sources describe pre-threshold (“predictive”) alerts and expanded in-transit visibility, but we did not find peer-reviewed evaluations or publicly accessible Illinois program documentation showing provider deployment of predictive alerts or weather-linked excursion prediction. In light of short warming intervals and observed outage exposures, preparedness planning in Illinois is best calibrated to plausible local outage windows rather than system-wide averages, consistent with CDC/IDPH guidance.

Looking ahead, three priority evidence needs emerge from this review. First, publicly accessible, cause-coded statewide aggregated data (temperature excursions and doses affected attributed to weather/power vs. other causes) would reduce ambiguity between “no events” and “no detection” and enable cross-jurisdiction learning. Second, statewide performance descriptions using clear, public metrics, coverage (e.g., share of enrolled providers with continuous monitoring, connectivity-resilient reporting, approved backup storage/transfer plans), timeliness (e.g., time to detect/respond and to restore safe storage or redistribute vaccine), and equity (e.g., outcomes in rural/high-outage areas), would allow external stakeholders to assess progress over time. Third, contextual evaluations of emerging monitoring tools in Illinois settings, including feasibility, costs, and any integration of weather/grid forecasts with storage unit-level risk, would clarify what adds value in practice. These are not prescriptions; they follow directly from the gaps identified in publicly accessible sources and align with the paper’s focus on weather-related risk to vaccine viability.