A new clinical study shows promising results of a Phase III chikungunya vaccine trial, the first time the shot has been tested in humans. If approved by regulators, the vaccine would have the capacity to protect millions of people from the debilitating mosquito-borne disease, authors explained in the study published June 12 in The Lancet.
First discovered in Tanzania in the 1950s, the viral disease has since spread to various parts of Africa, Asia, the Caribbean, and South America.
Symptoms include severe joint and muscle pain as well as high fever and skin rashes. There is currently no specific antiviral therapy. While symptoms usually improve within a week, joint pain (arthralgia) can persist for months. In some cases, lasting arthralgia can lead to debilitating chronic rheumatic arthritis disease.
“Chikungunya is fatal in very few cases, but the disease is not pleasant. You can be sick for two weeks. In addition, in severe cases, you get very painful arthritis that can last for weeks,” said Peter Kremsner, a specialist in infectious and tropical diseases at Tübingen University in Germany.
Chikungunya virus found in equatorial countries
Tropical regions currently see the highest rates of the virus, with Paraguay, Brazil, Bolivia, and Thailand most affected. Global cases are relatively low, with Paraguay experiencing the most at 82,240 cases and 43 deaths between January and March 2023. Thailand saw 259 cases and no deaths in the period.
There are reports of chikungunya virus cases in African countries, but up-to-date infection data is difficult to verify. Outbreaks have been ongoing in Congo, Sudan, and Kenya since 2018, but cases have been relatively low — Sudan, the most affected country in Africa, has only seen around 14,000 cumulative cases since 2018.
However, a major 2013 outbreak of chikungunya in South America led to over one million infections in just a few months. While death rates were low, around 52 per cent of infected people experienced severe joint pain lasting months.
Studies suggest the disease caused the loss of 1,50,000 disability-adjusted life-years in 2014 alone. The measurement represents the loss of the equivalent of one year of full health.
Chikungunya vaccine a first
The new Lancet study represents the results of the first Phase III trial conducted for a vaccine against the disease. According to the study, 28 days after a single vaccination with “VLA1553,” the vaccine resulted in virus-neutralising antibody levels lasting up to 180 days in 98.9 per cent of study participants.
“[Chikungunya] vaccination has shown very good efficacy in studies to date. After vaccination, a protective immune response can be detected in almost all vaccinated individuals after four weeks,” said Torsten Feldt, an infection and tropical disease specialist at University Hospital Düsseldorf, Germany.
The vaccine contains a modified, live version of the chikungunya virus that can replicate in the body without causing severe illness. Live vaccines closely mimic natural infections, triggering a robust immune response that provides long-lasting and broad protection.
They are very common—inoculations against measles, mumps, and rubella (MMR combined vaccine); smallpox; and yellow fever are all live vaccines.
However, there are potential risks associated with these types of vaccines, including the rare possibility of the weakened virus reverting to a more virulent form. However, the clinical trial showed the VLA1553 vaccination was well tolerated, including by older patients.
“Only a few relevant side effects occurred. Thus, the tolerability is comparable to other live vaccines. Although several thousand people have been vaccinated, monitoring of safety even after possible approval is important to obtain more accurate information also on rarer side effects,” said Feldt.
Live vaccines are just one of several types of vaccines designed to teach your immune system how to fight off diseases. Other types of vaccines include inactivated viruses, which are used for flu or rabies vaccines; messenger RNA (mRNA) vaccines, used for some COVID-19 vaccines and toxoid vaccines, used for diphtheria and tetanus vaccines.
In 2018, the chikungunya virus was listed as a priority pathogen for vaccine development by the World Health Organization (WHO).
Climate change is spreading insect-borne diseases
Chikungunya virus is currently only common in countries with tropical climates south of the equator. However, climate change is driving disease-carrying mosquitos closer to the poles, meaning the new vaccine could become applicable for larger populations around the world.
“The Asian tiger mosquito, which transmits the virus, is spreading more and more. This mosquito species is already native to southern Europe, and it is becoming increasingly common in Germany,” Kremsner said.
Malaria is a prime example of how increasing global temperatures are causing disease-spreading mosquitos to expand their territories. Between 1898 to 2016, species of malaria-carrying Anopheles mosquitoes have expanded their range by 4.7 km (3 miles) per year south of the equator—which amounts to around 550 km in total during that period.
Modeling data also predicts that rising global temperatures will further increase the poleward expansion of mosquito species, amplifying the risk of mosquito-borne diseases in more of the world’s population.