Climate change heightens the need for vaccines and impedes their delivery

This story was originally published by Inside Climate News and appears here as part of the Climate Desk collaboration.

Climate change is altering the world’s disease landscape, cultivating conditions ripe for human illness to spread in new places. A growing body of research shows it’s also disrupting one of the most effective tools to protect public health: vaccines. 

The World Health Organization (WHO) estimates that global immunization efforts have saved more than 154 million lives over the past five decades. However, extreme weather and global warming can destroy crucial vaccine stocks, impede transport and distribution and reduce effectiveness, according to a new study published in the journal Nature Climate Change. 

Meanwhile, hesitancy to accept vaccination rose sharply across the board in the aftermath of the COVID-19 pandemic, and a contingent of global politicians continues to express anti-vaccine rhetoric, including Robert F. Kennedy Jr., tapped by President-elect Donald Trump to lead the Department of Health and Human Services during his administration. Experts say that these combined factors create a “perfect storm” that could leave people less protected in the new era of climate-fueled disease. 

Climate-Related Disease Outbreaks: In many regions, the warmer and wetter conditions brought by climate change allow bacteria to thrive. Low-income countries are often the hardest hit. 

Cholera—a severe intestinal disease—is a prime example. Since 2021, there has been an uptick in cholera outbreaks across the globe, exacerbated by extreme weather, according to the WHO. In Africa, major flooding and above-normal hurricane seasons have increased outbreak severity and regional spread by giving ample opportunity for the disease-causing bacterium Vibrio cholerae to spread into drinking water. 

“Cholera in Africa is a climate change issue,” Jean Kaseya, director general of Ethiopia-based Africa Centres for Disease Control and Prevention, said earlier this year.

A 2022 study found that more than half of known human pathogenic diseases can be aggravated by climate change. This includes many vector-borne illnesses such as dengue and malaria, which are projected to spread to new areas as rising temperatures and increased rainfall create more favorable breeding conditions. 

Following Hurricanes Milton and Helene in September and October, Florida saw a small rise in dengue fever cases as mosquitoes thrived in the standing water left behind by flooding. Puerto Rico is in the midst of a severe dengue outbreak, with more than 3,000 cases as of September 2024—over double the number reported in 2023. Research presented at the annual meeting of the American Society of Tropical Medicine and Hygiene earlier this month projects that climate change could be responsible for a roughly 60 percent increase of dengue cases by 2050, NBC News reports. 

“Climate change is already reshaping infectious disease patterns by altering underpinning factors like temperature, rainfall, and species distribution,” Alessandro Siani, a researcher at the University of Portsmouth who studies vaccines, told me over email. 

The Impact on Vaccines: Many diseases such as cholera and dengue can be prevented or mitigated by vaccines. However, the same conditions that allow bacteria and vectors to thrive can threaten vaccine supplies. 

High temperatures denature certain vaccine proteins, which can decrease their effectiveness. Many vaccines, such as some COVID-19 shots, require storage at near-freezing temperatures to prevent degradation. That poses a major challenge if an outbreak occurs during extreme weather events such as a heat wave or hurricane, which could damage infrastructure and cause blackouts that shut down freezers. Additionally, climate-fueled changes in rainfall and humidity could deteriorate vaccine formulations and reduce shelf life, the new Nature Climate Change study points out. 

While climate change can cause “physical damage on the vaccines itself,” it can also impact a person’s ability to process immunization, study co-author Yongqun “Oliver” He, a professor at the University of Michigan Medical School, told me over Zoom. “If the environment is too hot or too cold, then the human’s response may change.”

During warmer spring and summer months, individuals can be more likely to experience dehydration or fever, which could “contribute to reported adverse events such as dizziness and fatigue” following a vaccine shot, according to the new study. A 2018 experiment on mice found that high external temperatures—such as those during a heat wave—dampened the animals’ adaptive immune responses to a flu virus. He says that more studies are needed to determine how the human body may respond to vaccines differently under warming conditions. 

Though vaccines are increasingly important in the face of climate change, confidence in their effectiveness and safety is declining for certain groups. A January study found that vaccine misinformation is rampant on social media and can have a strong influence on a person’s willingness to accept them. On top of this, political leaders and anti-vaccination nonprofits have organized widespread campaigns in recent years to discredit immunization, Politico reports. 

“The problem is that vaccine misinformation and disinformation have been spreading unchecked in some online platforms, and the discourse surrounding immunisation has been polarised for political and economic gain by unscrupulous individuals and groups,” Siani said in his email to me. “Unfortunately, we’ve seen several instances of populist politicians stoking anti-scientific and anti-intellectual rhetoric to gain political advantage, eroding public trust in scientists and healthcare workers.”

Kennedy has long been one of the most outspoken vaccine skeptics in the U.S., platforming debunked conspiracy theories such as the unproven link between vaccines and autism. However, in an interview with NPR after the presidential election, he assured listeners that he is “not going to take vaccines away from anybody.” In a separate interview with NBC News, he denied the notion that he is “anti-vaccine.” 

If confirmed as the head of the Department of Health and Human Services, Kennedy would have influence over how health agencies such as the Centers for Disease Control and Prevention regulate vaccines and could request lower funding for vaccine programs. Kennedy has not released a formal strategy in this space yet but alluded to his goals on the social media platform X in October: “I just want to be sure every American knows the safety profile, the risk profile, and the efficacy of each vaccine. That’s it.” 

Research shows politicians and scientists can play a strong role in peoples’ decision to take a vaccine—or reject them altogether. That decision could have profound implications for public health as rising temperatures continue to fuel disease spread, Siani said. 

“Vaccine hesitancy and climate change denialism are two faces of the same ugly coin—the public being manipulated into acting against their own wellbeing by domestic and foreign groups who stand to benefit from spreading misinformation,” he said. “Governments and policymakers must lead by example by demonstrating irreproachable transparency and accountability, particularly with regards to matters that affect public health.”