A major vaccine maker has warned that global warming is helping widen the spread of tick-borne encephalitis (TBE) and chikungunya, raising fresh concerns that diseases traditionally concentrated in specific regions could increasingly threaten populations in new parts of the world.
Paul Chaplin, chief executive of vaccine manufacturer Bavarian Nordic, told Reuters that changing temperatures and milder winters are contributing to the expansion of disease-carrying ticks and mosquitoes.
The warning comes as the geographic footprint of both diseases continues to change. TBE is moving northward in Europe, while chikungunya — traditionally associated with tropical and subtropical regions — is increasingly appearing in Europe and has the potential to spread further in the United States.
The shift is also being reflected in vaccine demand. Bavarian Nordic reported that sales of its chikungunya vaccine Vimkunya surged 415% in the second quarter, while revenue from its TBE vaccine Encepur increased 58%.
For public-health authorities, the development highlights a growing challenge: climate conditions can alter the habitats, survival and seasonal activity of the mosquitoes and ticks that transmit infectious diseases.
TBE risk map expands as ticks move north
Tick-borne encephalitis is a viral infection transmitted primarily by infected ticks and, in some regions, through consumption of unpasteurised dairy products. Severe infections can affect the central nervous system and cause inflammation of the brain and spinal cord.
Germany is emerging as an important example of the changing TBE landscape.
Chaplin told Reuters that the number of German regions considered at risk of TBE is increasing year after year.
“The number of regions in Germany that are now considered to be at risk of TBE increases year after year.”
He said the disease is moving north from its traditional stronghold in southern Germany, while TBE is also increasing in Scandinavia.
According to Germany's Robert Koch Institute (RKI), 693 TBE cases were reported in 2025, making it the country's third-highest annual total since nationwide data collection began in 2001. The institute also added two new TBE risk areas.
Chaplin attributed the changing distribution partly to warming temperatures and milder winters, which can create more favourable conditions for tick populations to survive and spread.
The development matters because expanding tick habitats can expose populations in newly affected areas to a disease for which local awareness and preparedness may previously have been limited.
Chikungunya moves beyond its traditional range
The second warning concerns chikungunya, a mosquito-borne viral disease that can cause fever and severe joint pain.
Historically associated with parts of Asia, Africa and the Americas, chikungunya is now appearing with increasing concern in Europe.
Chaplin said mosquitoes capable of transmitting the virus are already present in Europe and that infected travellers can introduce the virus into areas where those mosquitoes are established.
Previous locally acquired outbreaks have occurred in Italy and France, while France has reported locally acquired cases this year, according to the European Centre for Disease Prevention and Control.
Chaplin warned that the disease could eventually become more prevalent in southern Europe and the United States.
“It's probably only a matter of time until chikungunya, unfortunately, is prevalent in southern Europe, but also in the States.”
The concern is not that the virus has suddenly appeared in these regions. Rather, the combination of international travel, established mosquito vectors and favourable environmental conditions can create opportunities for local transmission after an infected person arrives from an affected area.
Why global warming matters for mosquito-borne diseases
Temperature is a critical environmental factor in the transmission of chikungunya.
The European Centre for Disease Prevention and Control (ECDC) says ambient temperature is among the most important environmental factors influencing mosquito-borne chikungunya transmission.
Warmer conditions can affect mosquito survival, activity and the replication of viruses inside mosquitoes, potentially influencing when and where transmission can occur.
The expansion of Aedes mosquitoes in Europe has therefore become an increasing public-health concern. These mosquitoes can transmit chikungunya as well as other viruses, including dengue.
The result is a complex interaction between climate change, vector expansion, international travel and urbanisation.
A warming climate does not create chikungunya or TBE, but it can change the environmental conditions under which their vectors survive and transmit infection.
Vaccine demand sends another warning signal
The infectious-disease warning is being accompanied by a striking increase in demand for vaccines.
Bavarian Nordic said second-quarter sales of Vimkunya, its chikungunya vaccine approved in the US and European Union in February 2025, jumped 415%.
Revenue from its Encepur TBE vaccine increased 58% during the same quarter.
The figures provide a glimpse into how changing disease risks are affecting the travel-health and vaccine markets.
For decades, vaccination against certain vector-borne diseases has largely been associated with travellers visiting areas where those infections are endemic. But the expanding geographic range of disease vectors could increasingly make local public-health preparedness relevant as well.
Europe already seeing local chikungunya transmission
The chikungunya warning has particular significance because Europe is no longer dealing solely with imported infections.
The ECDC has documented previous local transmission in European countries, including France and Italy, where competent mosquito populations can support transmission when infected people introduce the virus.
France has again reported locally acquired chikungunya infections this year, demonstrating that the conditions required for transmission can occur in parts of Europe.
This creates a potential cycle of concern: international travel can introduce the virus, established mosquitoes can transmit it locally, and suitable temperatures can allow transmission to continue.
For health authorities, early detection and surveillance are therefore becoming increasingly important.
A changing map of infectious diseases
The warning from a vaccine manufacturer comes alongside a broader scientific and public-health concern about the changing distribution of vector-borne diseases.
TBE's expanding risk areas in Germany and the northward movement of ticks illustrate how changes in temperature and winter conditions can influence tick-borne infections.
Chikungunya provides another warning. A disease historically associated with warmer regions is now capable of causing locally acquired outbreaks in parts of Europe where its mosquito vectors have become established.
For countries and health systems, the implications extend beyond vaccines.
Mosquito and tick surveillance, laboratory diagnosis, public awareness, vector control, travel-health advice and appropriate vaccination strategies could all become increasingly important as disease risks evolve.
And the concern is not limited to Europe.
Chikungunya is already present in countries across Asia, Africa and the Americas, meaning climate-driven changes in vector distribution could potentially alter transmission patterns across multiple regions.
The next health threat may not stay where it started
The emerging picture is increasingly difficult to ignore: the geographic boundaries of infectious diseases are not fixed.
As global temperatures rise and winters become milder in some regions, mosquitoes and ticks may find new environments in which they can survive and reproduce.
That does not mean every newly suitable area will experience sustained transmission. Disease spread depends on multiple factors, including the presence of competent vectors, infected individuals, population immunity, environmental conditions and public-health response.
But the combination of expanding vectors and changing climate conditions is creating new opportunities for diseases to cross traditional geographic boundaries.
For Paul Chaplin, the trend is already visible in the changing TBE map across Europe and the emergence of chikungunya transmission farther north than traditionally expected.
For public-health authorities, the message is equally clear: monitoring where mosquitoes and ticks are moving could become just as important as monitoring where the diseases themselves have historically been found.
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