Reflecting on 2024: Conflict, climate and new pathogen strains shaped global disease trends

As 2024 draws to a close, Airfinity has published its assessment of global infectious disease trends throughout the year. 

Dengue cases reached a record high of 13 million. Pertussis, also known as whooping cough, saw cases rise by 990% and a new, more deadly mpox strain emerged. H5N1 bird flu spilt over to a number of mammal species, including cattle causing large outbreaks in the US and raising concerns about its future pandemic potential in humans.

Diseases on the rise

The chart below highlights diseases which have seen a significant surge in the size and scale of outbreaks. Conflict, climate change, falling vaccination rates and new pathogen strains are all likely to have impacted trends throughout the year. Our analysis uses data from 128 sources from 206 countries.

Dengue: Record-high incidence

For the second consecutive year, dengue fever reached record highs across the Americas and Europe. Factors such as extreme temperatures and the El Niño climate phenomenon contributed significantly to the surge. With 2024 officially recognised as the hottest year on record, global temperatures exceeded 1.5°C above pre-industrial levels, which allows for the expansion of vector habitats that were previously unsuitable.

H5N1 Avian Flu: A rising threat

This year, human H5N1 avian flu cases increased by 525%, raising concerns about its potential as a public health emergency. 75 human infections were reported in 2024, with 61 cases in the United States, primarily linked to infected dairy cattle in California. The majority of animal infections have been reported in dairy cow herds in the United States and poultry and wild birds across Europe and Asia.

Whooping cough comeback

Despite an 990% rise in cases of pertussis, or whooping cough, the bacterium has likely returned to its normal epidemic cycle after years of disruption during the pandemic. 

Declined immunity, decreased vaccine coverage, and improved testing post-pandemic are all contributing to the surge in reported cases, as well as the growing prevalence of more virulent and vaccine escapable strains.

Mpox: Spread of a new clade

A more transmissible and potentially lethal clade of mpox, known as clade 1b, emerged this year. Initially identified in the Democratic Republic of Congo (DRC), the outbreak has spread to neighbouring countries, including Burundi, Kenya, Uganda and Rwanda, posing regional and global threats. The novel clade has so far been detected in eight countries outside Africa, mainly through importation from affected African countries and leading to two clusters of household transmission, one each in the UK and Germany.

Measles resurgence

Our analysis above shows global measles cases declined by 18% this year. However, there is a significant reporting lag with the available data from the WHO. When complete data is released, we expect any decline will be negligible, or the 2024 total may even surpass last year’s cases. This year, Europe reported a 147% increase, while the United States saw a 380% rise in measles cases, according to national data sources. 

Declining immunisation rates have led to a worrying resurgence of measles, a preventable yet highly contagious disease. Vaccination rates declined the most in the Eastern Mediterranean, Southeast Asia, and Oceania. These areas are at risk of future outbreaks and strategies to increase vaccination rates will be crucial.

Other key disease trends

Oropouche fever cases increased substantially, driven by improved surveillance, favourable climate, and a new, yet-to-be-studied strain. Evidence suggests this strain has expanded the vector range, enabling the pathogen to spread from rural areas to densely populated urban centres and extend its reach beyond the Amazon basin, affecting populations with limited immunity due to low prior exposure.

Polio has seen a resurgence in recent years, with cases rising 488% in 2024. The outbreaks were isolated to the two remaining countries where wild type polio is still endemic, Afghanistan and Pakistan. Contributing factors include the forced repatriation of Afghan nationals, leading to large-scale population movements this year. The disruption of vaccination campaigns due to military conflicts and attacks on vaccination teams, particularly in Pakistan, hampered containment efforts. These issues are expected to sustain elevated disease incidence until childhood immunisation challenges are resolved. Cases of vaccine-derived polio have been reported in Africa, Israel, Indonesia, Yemen and Gaza. 

Rwanda reported its first-ever outbreak of Marburg virus, a rare but severe disease, in September 2024. The outbreak resulted in 66 confirmed cases and 15 deaths, making it one of the largest documented to date, although with the lowest case-fatality rate ever documented. Rwanda’s proactive response to the new challenge, including the rapid implementation of comprehensive outbreak surveillance, rapid deployment of investigational vaccines and treatment resource mobilisation, was instrumental in curbing the spread of the highly lethal disease and serves as a model response for infectious disease emergencies.

Diseases which declined

While some diseases surged, Airfinity data also show a notable decline in others, including Crimean-Congo hemorrhagic fever (CCHF), and West Nile fever. These declines have been influenced by improved public health interventions, climate variations, and human-driven factors. 

It is important to note, that though the overall global trend shows a decline, there may be increases on a country level.

Deadliest outbreaks of 2024

Airfinity has identified the year’s deadliest outbreaks, those posing significant risks due to their scale and severity. 

Dengue in Brazil

Brazil saw nearly 6,000 deaths from dengue in 2024, a 405% increase from last year. This rise is attributed to extreme weather events that foster mosquito breeding, rapid urbanisation, and environmental degradation.

Re-emergence of Cholera

The year’s deadliest outbreak was on the island of Comoros in East Africa. Cholera re-emerged in Comoros this year after over 15 years, triggered by the arrival of a boat from Tanzania, resulting in nearly 11,000 cases and 152 deaths. The outbreak marked a significant health crisis for the island, with a novel highly-resistant strain contributing to the high morbidity and mortality, which has been linked to other outbreaks in East Africa.

Cholera outbreaks have been reported in 32 other countries in 2024, mainly limited to the African continent, particularly East Africa. Overall, the global population affected by cholera this year remains lower than 2023, however, the number of deaths is higher, influenced by challenges in outbreak response led by conflict, displacements, and climate change. An example is Yemen - one of the world’s worst humanitarian crises, which is the global leader in cholera morbidity in 2024, accounting for over a third of cases. Similarly, Afghanistan has reported concerningly high disease levels, while the situation is worsening rapidly in Sudan and South Sudan due to ongoing conflict and refugee crisis.

West Nile Fever in Israel

West Nile fever (WNF), a mosquito-borne illness with no available treatment, surged to a record year high in Israel with 74 deaths recorded, the highest case-fatality rate among WNF outbreaks in 2024. 

With record-high temperatures in June, the mosquito season started early. The impact of conflict in the area has also led to poor living conditions, disrupted waste management and increased standing water. WNF has also increased in several other European countries including Greece, Romania, Italy and Spain.

Looking ahead

2024 reflects how conflict, climate change, declining vaccination rates, and emerging health threats are shaping the global disease landscape. While progress has been made in some areas, the rise of preventable and climate-sensitive diseases highlights the need for renewed focus on prevention, surveillance, and global collaboration.

What will 2025 bring? Will outbreaks grow or will medical advancements be enough to contain growing threats? Airfinity’s forecasting and modelling tools aim to address these questions by providing data-driven insights into bio-risks and effective countermeasure strategies. 

While technologies are advancing, countermeasure uptake and equitable access are increasingly important. Vaccine uptake remains the primary limiting factor in population-level vaccine efficacy. Forecasting models identify high-risk outbreaks and regions, predict countermeasure impact, and guide evidence-based decisions, enabling more effective and timely responses to global health threats. As we step into the new year, addressing these questions will be critical to safeguarding global health.