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Executive summary
Chikungunya is an exceptionally painful though rarely deadly mosquito-borne disease. Its prevalence is expanding as climate change spreads the range of the mosquitoes which carry it.
Disease basics
Chikungunya is a mosquito-borne disease caused by the chikungunya virus (CHIKV; see ECDC fact sheet, US CDC fact sheet, and WHO fact sheet). Symptoms of acute chikungunya include a rapid-onset high fever, severe joint pain, joint swelling, muscle pain, headache, nausea, fatigue and rash. The incubation period is usually 3-7 days, with a range of 1-12 days, and symptoms typically last about 10 days. Approximately 15%20and%20joint%20pains.)-40% of CHIKV infections are asymptomatic. A recent study estimates a burden of disease of 17.8M cases annually, about a fifth of dengue’s.
Reports of people who have had the disease describe it as exceptionally painful. However, the case fatality rate (CFR) is ≤0.1%, similar to that for seasonal flu. Infants, especially newborns (age <30 days, CFR 3.8% in 2022-2023 in Paraguay), and, to a far lesser extent, elderly people with other health problems (CFR 0.6% among people aged ≥80 years in 2022-2023 in Paraguay) face the greatest risks of severe disease and death.
There is no specific antiviral treatment for acute chikungunya. According to the WHO, treatment “includes addressing fever and joint pain with anti-pyretics and optimal analgesics, drinking plenty of fluids and general rest. ... Paracetamol or acetaminophen are recommended for pain relief and reducing fever until dengue infections are ruled out, as non-steroidal anti-inflammatory drugs (NSAIDs) can increase the risk of bleeding.”
In addition to acute disease, CHIKV infection often causes long-term health problems as well. About 30-40% of people who get chikungunya have recurrent joint pain, in some cases for years. Rarely, myocarditis, hepatitis and ocular and neurological disorders can develop.
Vaccines
Two vaccines are approved for use in populations at risk, but they aren’t widely available. And the license for one of them, Ixchiq, was just suspended in the US, after administration in adults age ≥60 was paused in May because of serious safety concerns; the US FDA states that “one death from encephalitis directly attributable to the vaccine” and over 20 serious cases of chikungunya-like illness have been reported for the live-attenuated vaccine. However, the vaccine manufacturer states that recent adverse vaccine effects are "consistent with those previously reported during clinical trials and post-marketing experience." After imposing a similar license restriction in May, the European Medicines Agency lifted its temporary restriction on July 25.
Both vaccines currently in use appear likely to be very effective against infection. Phase 3 clinical trial data show that the Ixchiq vaccine elicits protective levels of antibodies in 97.8% of study participants 28 days after vaccination, which persists in 96% of participants at 6 months after vaccination, and 95% of patients four years afterwards. The second vaccine, Vimkunya, a virus-like particle vaccine, elicited protective antibodies pro in 98% of clinical trial participants aged 12–64 years and in 87% of participants aged ≥65 years, 3 weeks after vaccination. The percentages of study participants with protective levels of antibodies fell to 85% and 76% for the two age groups, respectively, after 6 months.
Several other vaccine candidates are in varying stages of development.
Where and how does chikungunya spread?
Large outbreaks and sporadic cases of chikungunya currently occur in the Americas, Asia and Africa, and small outbreaks occasionally occur in Europe. CHIKV was first identified in Tanzania in 1952 and has since spread around the world. It has been detected in >110 countries to date.
Non-human primates in Africa, bitten by forest-dwelling Aedes mosquitoes, are the original, natural reservoirs of CHIKV. Now, humans are the largest reservoir of CHIKV.
Both Aedes aegypti or Aedes albopictus (“Asian tiger”) mosquitoes carry the virus and are responsible for most transmission. Local mosquito-borne transmission in humans has been seen in all regions of the world with established populations of these mosquitoes. Both species bite humans primarily during the daytime, and while both species bite outdoors, Ae. aegypti also bites indoors.
Chikungunya can also spread through blood transfusions or other interactions with infected blood. It can also be transmitted in pregnancy to a fetus, or at birth to a newborn. CHIKV has not been found in breast milk.
In China
Chikungunya saw an outbreak in China this year, developing from 478 cases by the 17th of July, 3K cases by the 24th of July, 10K cases by August 8th. Monthly data for September is not yet out.
Although larger, China is further apart culturally, and thus granular data on disease spread is harder for us to find. Initial English-language reporting seems to have stemmed from a warning from the CDC in Hong Kong. Because of better data availability we turn to looking at this years’ chikungunya outbreak in Europe:
In Europe
In the short term
Chikungunya continues to spread in Europe. As of August 27, 227 cases have been confirmed in Italy, and 63 cases in France in 2025. Many in Europe are wondering, how much is chikungunya going to spread, and when is it going to stop? In the short-term, this year, not much.
First, let’s look at previous outbreaks in Europe. Six outbreaks with local spread have been reported in Europe before the current outbreak, with the first outbreak occurring in 2006. All of these outbreaks were in Italy, France or Spain. In four of these outbreaks, fewer than 20 cases of local transmission were reported; another outbreak saw over 200 suspected cases, and the largest outbreak to date saw nearly 800 confirmed and suspected cases. All of these outbreaks ended.
The fundamental reason why these outbreaks ended, and why the current outbreak will likely end soon, is that Ae. aegypti is absent in nearly all of Europe, and while _Ae. albopictus _is established in much of southern Europe, _Ae. albopictus _adults generally die off in the fall in Europe. When the adult mosquitoes die, transmission stops, and outbreaks end.
(Sadly The Motte doesn't allow for images, so just giving the source) (Source: https://www.ecdc.europa.eu/en/publications-data/aedes-albopictus-current-known-distribution-june-2025 )
(Source: https://www.ecdc.europa.eu/en/publications-data/aedes-aegypti-current-known-distribution-june-2025 )
Currently, chikungunya case clusters are active in northern Italy (Bologna, Verona and Modena provinces), one unspecified province in Italy, and in over 20 departments throughout southern, western and northeastern France. Ae. albopictus adults are likely to die off in all of these regions over the coming weeks to months, as temperatures become inhospitably cold. And when the adult mosquitoes die, chikungunya will stop spreading in Europe.
Spatial distribution of locally acquired chikungunya virus disease cases in 2025 through 27 August 2025:
(Source: https://www.ecdc.europa.eu/en/chikungunya-virus-disease/surveillance-and-updates/seasonal-surveillance )
And here is this same map as of the 2nd of October; it has spread a bit further:
Some Ae. albopictus populations in Europe are starting to become adapted to the cold, including some populations in Rome, Italy and the Region of Murcia, Spain. So it’s not impossible that some transmission could continue in southern France or perhaps in new, more southern areas of Europe.
Forecasters think there’s an x% chance (range, y% to z%) that the current outbreak in Europe will end this fall rather than continue through winter and into 2026.
In the United States?
Last week, authorities reported on a local case in New York, i.e., not associated with travel. The CDC page on Chikungunya in the US doesn’t yet confirm it, but it hopefully will be a good page to watch for an increasing number of cases—although recent cuts from the Trump administration might have left the CDC somewhat under-resourced.
The big picture: shifting climate patterns will change the distribution of diseases
At Sentinel, we have been tracking potentially worrisome diseases in our weekly brief over the last year. In general, we are seeing many diseases, particularly those originally tropical, expand and shift their geographic ranges as a result of climate change. Europe becoming more hospitable to mosquitoes leading to the spread of chikungunya is just one example. In the US, we saw the spread of the West Nile Virus, also a mosquito-borne disease.
Beyond mosquito-borne diseases, Spain and Greece faced alerts due to rising cases of Crimean Congo haemorrhagic fever (CCHF), spread by ticks. In the US, cases of alpha-gal syndrome exploded, carried by ticks described as “a cross between a lentil and a velociraptor”. In general, we are seeing many diseases expand and shift their geographic ranges as a result of climate change.
Looking to the longer term, it looks very likely that chikungunya transmission will eventually occur year-round, as warmer conditions in Europe expected with climate change will likely allow Ae. albopictus adults to survive all year. Chikungunya will likely become established in Europe, as it is on other continents.
A big unknown is the impact of the changing Atlantic meridional overturning circulation (AMOC), which normally warms Europe but which could slow down or collapse. If it does so, Europe would become colder, stopping the spread of mosquito-borne diseases.
Overall, Chikungunya in particular doesn’t seem like a COVID-level risk, but the shifting pattern of diseases as a whole seems [statement of severity]
Some possible forecasting questions my team might forecast on:
I might also add a statement that my team may or may not trade on the above, in the style of Hindenburg research, because I think it's cool. But the play, if any, probably involves buying the stocks of the vaccine makers next year once it has faded from salience and before it fades into view again in Europe's/the US's summer.
Disease free but starving and freezing to death.
I mean, yeah, in a full collapse. But it's tricky to know how likely that really is. Like, if I see papers like https://iopscience.iop.org/article/10.1088/1748-9326/adfa3b and https://www.nature.com/articles/s41467-023-39810-w, unclear whether these are dire warnings I really need to pay attention to, or trends that are exaggerated by ideologically captured scientists who have the incentive to overexaggerate the importance of their own research. Matters in real life decisions, too, as I'll soon be buying a house in Paraguay
AFAIK the degree of warming usually expected to stop AMOC is generally on the same degree or even higher than the cooling expected to result from the stop, so it mostly comes out as a wash except for slightly more winter extremes, but which are still limited to ca -10 °C. In general also, higher co2 + higher temperatures also mean plants grow better, (which we can already see with current levels) so I don't think starving will be a particular issue.
As someone living in northern germany, I'd certainly welcome a bit more snow in winter!
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