On 20 October 2026 the MHRA published a Drug Safety Update confirming that the UK marketing authorisation for IXCHIQ, Valneva's single-dose live attenuated chikungunya vaccine, has been withdrawn on advice from the Commission on Human Medicines (CHM). The regulator concluded that, for UK travellers, the benefits no longer outweigh the risks.
The decision did not rest on a brand-new signal. It is the end point of an 18-month escalation driven by post-marketing reports of vaccine-strain chikungunya-like illness and encephalitis, some fatal. What changed was the weighing: restrictions by age and comorbidity had not contained the risk, while the benefit for short-term travellers stayed modest and a non-live alternative exists.
The revocation is UK-only. Authorisations in the EU, Canada and Brazil are unaffected, which makes this a useful case study in context-dependent benefit-risk.
How we got here
IXCHIQ (VLA1553) went from first approval to UK revocation in under three years, with each regulator tightening use as serious post-marketing cases accumulated.
| Date | Regulator / actor | Action |
|---|---|---|
| 20 Oct 2026 | MHRA | Drug Safety Update: authorisation withdrawn, stock to be destroyed, travellers directed to alternatives |
| 7 Oct 2026 | Valneva | Announces UK revocation after CHM reassessment; disagrees but will not appeal |
| 11 Feb 2026 | MHRA / CHM | Permanent restrictions: not indicated at 60+, contraindicated with hypertension, cardiovascular disease, diabetes or chronic kidney disease |
| 22 Aug 2025 | FDA | US licence suspended after four further serious cases |
| 6 Aug 2025 | FDA | Pause for 60+ lifted with revised indication and enhanced warnings |
| Jul 2025 | EMA (PRAC) | Review closes; temporary 65+ contraindication lifted, warnings strengthened |
| Jun 2025 | MHRA | Precautionary pause in people aged 65 and over |
| May 2025 | EMA, FDA/CDC | PRAC review opened; temporary restriction in 65+ (EU) and pause in 60+ (US) |
| Feb 2025 | MHRA | UK authorisation granted; launched mid-2025 |
| Jun 2024 | EMA | EU authorisation |
| Nov 2023 | FDA | US accelerated approval on an immunogenicity endpoint |
Valneva's figures put worldwide use at about 187,000 doses, a modest exposure base for detecting rare events.
The previously known safety profile
At licensure, IXCHIQ looked like a well-tolerated vaccine with one class-specific caveat: as a live attenuated virus, it can cause a mild version of the disease it prevents.
Pivotal trial (VLA1553-301, The Lancet 2023). About 3,082 adults received a single dose. Seroresponse at day 28 was 98.9%, including in participants aged 65 and over. Serious adverse events occurred in 1.5% of vaccinees versus 0.8% on placebo; only two were judged vaccine-related (myalgia and SIADH), and both resolved. The trial was not designed to detect rare events in frail older adults.
Efficacy basis. Approval rested on a neutralising-antibody surrogate, not field efficacy. The FDA's accelerated approval required confirmatory studies that had not reported by the time of suspension.
Labelled risks after the 2025 reviews. The UK SmPC (updated March 2026) carried:
- severe or prolonged chikungunya-like adverse reactions (fever, arthralgia, myalgia)
- encephalitis, including fatal cases, from post-marketing use
- vaccine viraemia in week one, cleared by day 14, with a four-week blood-donation deferral
- contraindication in immunodeficiency; no use at 60+ or with hypertension, cardiovascular disease, diabetes or CKD
- a requirement for an individual benefit-risk assessment before every dose
Post-marketing signal, 2025. Reports emerged largely from the outbreak-response campaign in La Réunion, where older residents were vaccinated. By May 2025 the EMA counted 17 serious events, two fatal, in people aged 62 to 89; one death was encephalitis in an 84-year-old. The PRAC review later identified 28 serious cases and three deaths, concentrated in people 65+ with multiple or uncontrolled chronic conditions. The FDA reported 21 hospitalisations and three deaths, including one encephalitis death with vaccine-strain virus confirmed by PCR in cerebrospinal fluid. That case established causality beyond temporal association.
What the latest review found
The October 2026 decision reflects a re-weighing of accumulated post-authorisation data rather than a new type of adverse reaction. Valneva states that no new safety signal was identified; the MHRA's update does not claim one either.
The finding that mattered is about who was affected. The MHRA notes that the serious reactions, chikungunya-like illness and rare neurological events such as encephalitis, were mainly seen in older adults and people with underlying conditions, but also in individuals with no known health conditions. Some cases led to hospitalisation or death.
That sentence undercuts the February 2026 strategy. Those restrictions assumed the risk could be fenced off by age (60+) and four comorbidities. Cases in otherwise healthy recipients mean residual risk remains in exactly the population the label still allowed. One of the four cases behind the FDA suspension was in a 55-year-old, below every age cut-off then in force.
Open question: the MHRA has not published UK case counts, ages or reporting rates for the period since February 2026. Without them, the residual-risk estimate cannot be checked independently.
How the benefit-risk balance shifted
The balance tipped because each risk-minimisation step also removed benefit, until the remaining population had little to gain and a residual, unquantified risk of serious harm.
| Factor | At authorisation (Feb 2025) | At withdrawal (Oct 2026) |
|---|---|---|
| Target population | Adult travellers, no upper age limit | Travellers under 60 with none of four common comorbidities |
| Expected benefit | Highest in older adults, who face the worst chikungunya outcomes | Largely limited to younger, healthy travellers with low risk of severe disease |
| Efficacy evidence | Immunogenicity surrogate; field efficacy pending | Unchanged; confirmatory data still outstanding |
| Serious risk | Theoretical vaccine-strain disease; rare in trials | Confirmed vaccine-strain encephalitis and deaths; cases also in people without risk factors |
| Risk minimisation | Standard warnings | Age cap, four contraindications, mandatory individual assessment, judged insufficient |
| Alternatives | None licensed | Non-live virus-like-particle vaccine (Vimkunya) available; bite avoidance |
| Use in practice | Launch mid-2025 | Low uptake; Valneva had stopped active UK distribution |
Three points drove the CHM's conclusion.
- The benefit and the risk sat in the same people. Older adults stand to gain most from protection against severe chikungunya, and they were also most exposed to vaccine-strain harm. Excluding them made the vaccine safer but far less useful.
- Travellers have low, time-limited exposure. For a preventive vaccine in healthy people on a short trip, tolerance for fatal adverse reactions is low. A trip-length risk of wild-type infection rarely justifies a small but real risk of encephalitis.
- A non-live option changes the comparator. Once a vaccine without live virus is available, a residual vaccine-strain risk is no longer the price of protection.
The same data can support a different conclusion elsewhere. In endemic, outbreak-prone settings such as Brazil, background infection risk is far higher. Valneva cites a pilot campaign of over 61,000 vaccinations there without new signals. That explains why the EU, Canadian and Brazilian authorisations stand while the UK's does not.
Lessons for safety strategy
IXCHIQ shows how a product can lose its licence without a new signal, when risk minimisation erodes the benefit it was meant to protect.
- Test whether restriction preserves benefit. Before proposing an age cap or contraindications, map where benefit concentrates. If it overlaps the at-risk group, the restricted label may not stand up to reassessment.
- Plan for live-vector class risks from day one. Vaccine-strain disease and neurotropism are predictable for live attenuated vaccines. Trials sized for immunogenicity cannot rule out rare encephalitis in frail adults; the pharmacovigilance plan should target it explicitly.
- Watch off-label and outbreak use. The signal surfaced in a mass campaign in older residents, a population thin in the pivotal data. Emergency deployment needs active surveillance, not passive reporting alone.
- Surrogate-based approvals carry a time limit. With field efficacy unconfirmed, the benefit side of the balance never strengthened to offset emerging risk.
- Benefit-risk is context-specific. Traveller and endemic indications warrant separate assessments, and divergent regulatory outcomes should be anticipated in the risk management plan.
- Commercial context shapes the outcome. With low uptake and distribution already halted, the company chose not to appeal. Thin market presence lowers the cost of a regulator's precautionary call.
Sources
- MHRA Drug Safety Update: IXCHIQ UK marketing authorisation withdrawn (20 Oct 2026)
- MHRA Drug Safety Update: updates to restrictions of use (11 Feb 2026)
- MHRA news: additional restrictions for IXCHIQ (11 Feb 2026)
- IXCHIQ UK SmPC, emc (updated 4 Mar 2026)
- Valneva: Update on IXCHIQ in the United Kingdom (7 Oct 2026)
- EMA: review of Ixchiq started (May 2025)
- EMA: temporary restriction in 65+ lifted (Jul 2025)
- FDA: Ixchiq biologics license suspended (22 Aug 2025)
- Schneider et al., The Lancet 2023: VLA1553 phase 3
- Zonebourse via Option Finance: dose and Brazil pilot figures (8 Oct 2026)
- AABB: FDA suspension and Vimkunya context (Aug 2025)
This article is for information only and is not medical or regulatory advice.
Follow Safety Strategy on LinkedIn (opens in a new tab) for new articles and updates. Back to all news