FDA Suspends Licensing of Ixchiq Chikungunya Vaccine Amid Safety Concerns

On August 22, 2025, the FDA’s Center for Biologics Evaluation and Research (CBER) suspended the biologics license for chikungunya vaccine (Ixchiq; Valneva Austria GmbH), a live attenuated chikungunya vaccine previously approved under the accelerated pathway in November 2023 for individuals ages 18 years and older at high risk of exposure to the virus.¹ The decision followed serious post-marketing safety reports that raised new concerns about the vaccine’s benefit-risk profile.

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Since its approval, Ixchiq has reportedly caused over 20 serious adverse events (SAEs) ranging from hospitalizations to at least 3 deaths.² One of the most concerning cases involved encephalitis in which the vaccine strain of the chikungunya virus was detected in cerebrospinal fluid by PCR, suggesting direct vaccine-related viral replication.¹ These results led the FDA and CDC on May 9, 2025, to issue a temporary halt to the administration of chikungunya vaccine, live in adults ages 60 and older while further investigations were conducted.²

Although the FDA later lifted this pause on August 6, 2025, following the addition of enhanced safety warnings to the labeling, concerns persisted. The updated indication advised caution in adults ages 65 and older with chronic medical conditions, highlighting a population particularly vulnerable to severe outcomes.¹ Ultimately, the Center for Biologics Evaluation and Research determined that confirmatory trials had not yet verified clinical benefit and that the known and potential risks outweighed the expected benefits under most plausible scenarios, leading to the suspension of Ixchiq's license.¹

Ixchiq was the first approved chikungunya vaccine by the FDA, and this not only shows the vaccine's effectiveness but also indicates a significant step in preventing the spread of a disease that is present in over 110 countries.³ In pivotal clinical trials, the vaccine demonstrated efficacy but also showed a small proportion of recipients (1.6%) experiencing chikungunya-like symptoms that interfered with daily activities, and two individuals requiring hospitalization.² These early safety signals, although relatively rare, foreshadowed the more SEAs observed during post-marketing use.

Reports compiled in May 2025 described 17 serious adverse events worldwide among vaccine recipients ages 62 to 89 years, including 2 fatalities.² One case involved an 84-year-old male who developed encephalitis, and another involved a 77-year-old male with Parkinson’s disease whose deteriorating health after vaccination contributed to aspiration pneumonia and death. Six of these serious cases were reported in the United States. The FDA and CDC emphasized the need for pharmacists and other clinicians to carefully weigh risks and benefits in older individuals and to report suspected adverse events to the Vaccine Adverse Event Reporting System.² Pharmacists are urged to educate patients on these risks, especially in populations with underlying conditions.

While Ixchiq faces significant scrutiny, another vaccine, chikungunya vaccine recombinant (VimKunya, Bavarian Nordic), a virus-like particle vaccine, received FDA approval in February 2025 for individuals ages 12 and older.³ Phase 3 data demonstrated that 98% of recipients developed neutralizing antibodies by day 22, with durable responses seen in 86% at 6 months. In participants ages 65 and older, 87% still mounted strong antibody responses.³ Unlike Ixchiq, which uses a live attenuated virus, VimKunya’s VLP platform may offer a safer profile for vulnerable populations.

REFERENCES

1. FDA Suspends Biologics License for IXCHIQ (Chikungunya Vaccine, Live). U.S. Food and Drug Administration. Published 2025. https://www.fda.gov/safety/medical-product-safety-information/fda-update-safety-ixchiq-chikungunya-vaccine-live-fda-suspends-biologics-license-fda-safety

2. Gerlach A. Ixchiq Vaccine Linked to Fatal Adverse Events in Seniors, FDA and CDC Urge Caution. Pharmacy Times. Published May 13, 2025. https://www.pharmacytimes.com/view/ixchiq-vaccine-linked-to-fatal-adverse-events-in-seniors-the-fda-and-cdc-urge-caution

3. Gerlach A. Chikungunya Vaccine Receives FDA Approval for Individuals 12 Years and Older. Pharmacy Times. Published February 17, 2025. https://www.pharmacytimes.com/view/chikungunya-vaccine-receives-fda-approval-for-individuals-ages-12-and-older