Saint-Herblain, France - US health authorities have suspended the license for the Ixchiq vaccine against the chikungunya virus following reports of "serious adverse events," the drug's French maker said Monday.

Ixchiq is one of just two vaccines approved by the US Food and Drug Administration for the mosquito-spread virus, which mainly occurs in tropical and subtropical regions but has recently been discovered in countries worldwide.

French company Valneva obtained US approval for the vaccine in 2023, but reports of side effects have prompted reviews in particular over its use in older patients, including by the European Medicines Agency this year.

"The suspension of the licence is effective immediately," Valneva said of the FDA order issued Friday, citing four additional cases of serious side effects, three of which involved people aged 70 to 82.

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"As we determine potential next steps, and as the clear threat of chikungunya continues to escalate globally, Valneva remains fully committed to maintaining access to our vaccine as a global health tool," chief executive Thomas Lingelbach said in a statement.

The company said it was evaluating the financial impact of the suspension "but is not modifying its revenue guidance at this time."

It said Ixchiq generated sales of 7.5 million euros ($8.8 million) in the first half of this year.

The suspension prompted a sell-off of Valneva's shares on the Paris stock exchange, falling over 26% in opening deals.

Public health experts say chikungunya could be a potential future pandemic threat as climate change pushes the mosquitoes that spread it into new regions.

The symptoms are similar to those of dengue fever and Zika virus, with high fever and severe joint pain that is often debilitating and varies in duration.

Chikungunya is rarely fatal, though there is increased risk of death for babies and the elderly.

In July, the World Health Organization warned of the risks of a major chikungunya epidemic, calling for urgent action.

The agency said it was picking up the same early warning signs as in a major outbreak two decades ago, which swept across the Indian Ocean before spreading globally and affecting almost half a million people.

So far this year, Europe has seen 27 chikungunya outbreaks, a new record for the continent, the European Centre for Disease Prevention and Control (ECDC) said this month.