A vaccine for chikungunya—a mosquito-borne infection with similar symptoms to dengue and Zika—could finally be on the horizon after promising results from a late stage trial were published in the Lancet on Monday, a key towards tackling the emerging global health threat as climate change creates increasingly ideal conditions for the virus to spread explosively, including in the U.S.
Aedes mosquitoes can spread chikungunya.GETTY IMAGES
Valneva’s chikungunya shot, made from a weakened form of the virus and administered in a single dose, was safe, well-tolerated and provoked an immune response that indicates protection against disease, according to the firm’s late stage clinical trial published in the peer reviewed medical journal.
Researchers said the trial—which enrolled 4,115 healthy adults across the U.S., 3,082 of whom were given the vaccine—did not raise any safety concerns over the shot and Juan Carlos Jaramillo, Valneva’s chief medical officer, said an independent board evaluating the trial’s data and any adverse reactions reported afterwards came to the same conclusion.
Common side effects reported in the trial included headaches, fatigue, muscle and joint pain and pain at the injection site, which were consistent across different age groups.
As the study was conducted in the U.S., a region where chikungunya is not endemic, researchers measured the immune system’s response to test whether the vaccine protects against disease caused by infection with the virus.
Immune responses—tested in 362 participants, 266 of whom received the shot—were strong, the researchers said, with 99% showing antibody levels considered to protect against the virus 28 days after vaccination.
While antibody levels—which were similar for both younger and older subjects—fell after the 28 day mark, the researchers said protection persisted for 96% of vaccine recipients six months after getting the shot.
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WHAT TO WATCH FOR
The trial’s length meant researchers were not able to evaluate the protection the shot provided for periods longer than six months and they said a follow up study is already underway to test immune responses over five years. They said results from the one year point are encouraging. As a precaution, researchers are also keeping an eye on the risk of miscarriage following the shot, which was slightly higher among research subjects than the general population. While this could be down to the small sample size and be a natural statistical variation—two miscarriages were explained by genetic disorder or medical history while no reason could be identified for the other—and no safety concerns were flagged, the researchers said monitoring will be needed as the vaccine is rolled out.
WHAT WE DON’T KNOW
As the study was undertaken in the U.S., protection against chikungunya has been inferred from the immune response provoked by the vaccine. While antibody levels are predictive of protection against serious illness—antibodies are proteins that can block viruses from entering cells—they are only one aspect of the immune system and are relatively short lived and offer only a partial insight into a vaccine’s potential value. Studies in areas where chikungunya is endemic—spreading naturally and constantly present—will be needed to verify and expand the trial’s findings and see how it works in the real world. Important factors researchers are considering are its impact on children and teens—a trial is underway in Brazil—and whether existing or subsequent exposure to the virus will meaningfully alter responses to the vaccine. Writing in a linked comment article, Kathryn Stephenson, a researcher at the Center for Virology and Vaccine Research at the Beth Israel Deaconess Medical Center who was not involved in the study, said “real-world effectiveness studies in the context of actual” outbreaks will also be crucial to confirming the shot’s value.
The name chikungunya comes from the Kimakonde language, meaning “to become contorted” or “that which bends up,” a reference to the stooped or contorted posture of those infected with the virus on account of the severe joint pain it can cause. In addition to joint pain—potentially debilitating and can last for weeks, months or even years and develop into chronic arthritis—symptoms of chikungunya include fatigue, headaches and nausea and the infection is often confused with dengue and Zika, which have similar symptom profiles. While serious disease and death from chikungunya are rare—children and older people are at the greatest risk—the virus can still cause significant ill health in regions where it circulates, Aslam Khan, a clinical assistant professor of pediatric infectious diseases and global health faculty fellow at Stanford University, told Forbes. There are also no treatments directly targeting the virus and no approved vaccines. Valneva, which until recently was competing for primacy with Merck, is potentially in line to be first and its shot is being reviewed by the Food and Drug Administration and Canada’s health authority.
Chikungunya is spread by Aedes mosquitoes, which are typically found in warmer, tropical regions of the world and are responsible for spreading other viruses including dengue, Zika and yellow fever. There have been multiple outbreaks of chikungunya in various parts of the world this year, including parts of the Americas and Asia. Various health authorities and experts have identified it as an emerging threat to global health.
Khan told Forbes he considers the risk to the U.S. from chikungunya to be low but said he believes “that is changing.” Khan explained that we “have already found the mosquito vector within the United States and with climate change, ultimately there may be favorable conditions for ongoing growth and proliferation of those species. Humans can serve as a potential reservoir for the virus which can be picked up and spread by these mosquitoes,” he explained.