Sanofi’s Dengvaxia immunisation could worsen disease in some patients not previously exposed to virus

The Philippines has ordered an investigation into the immunisation of more than 730,000 children with a dengue vaccine that has been suspended following an announcement by French drug company Sanofi that it could worsen the disease in some cases.

The World Health Organisation said it hoped by the end of the year to conduct a full review of data on the vaccine, commercially known as Dengvaxia. In the meantime, the WHO recommended it be used only in people who had a prior infection with dengue.

Last week, the Philippines department of health halted the use of Dengvaxia. Brazil, where dengue is a significant health challenge, had already recommended restricted use of the vaccine.

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Dengue is a mosquito-borne tropical disease, killing about 20,000 people a year and infecting hundreds of millions.

Sanofi explained its “new findings” at a news conference in Manila but did not say why action was not taken after a WHO report in mid-2016 that identified the risk.

While Sanofi’s Dengvaxia is the first approved vaccine for dengue, scientists already recognised it did not protect equally against the four different types of the virus.

A new analysis from six years of clinical data showed Dengvaxia provides persistent protective benefit in those who had prior infection. But for those not previously infected, more cases of severe disease could occur following vaccination, Sanofi said.

Volunteers Against Crime and Corruption, a non-governmental organisation (NGO), said it had received information that three children who were vaccinated with Dengvaxia in the Philippines had died, and a prominent senator, Richard Gordon, said he was aware of two cases, but gave no details. He said approval and procurement for the programme was done with “undue haste”.

Health minister Gerardo Bayugo told Reuters the three referred to by the NGO died due to causes not related to the vaccine. Sanofi said no deaths had been reported.

“As far as we know, as far as we are made aware, there are no reported deaths that are related to dengue vaccination,” said Ruby Dizon, medical director at Sanofi Pasteur Philippines.

Sanofi said the long-term safety evaluation showed significantly fewer hospitalisations due to dengue in vaccinated people over nine years old compared with those who had not been vaccinated.

Nearly 734,000 children aged nine and over in the Philippines have received one dose of the vaccine as part of a programme that cost 3.5 billion pesos (£51.4m, US$69.54m). There was no indication that Philippines health officials knew of any risks when they administered the vaccination.

However, the WHO said in a July 2016 research paper that “vaccination may be ineffective or may theoretically even increase the future risk of hospitalised or severe dengue illness in those who are seronegative at the time of first vaccination regardless of age”.

Singapore’s Health Sciences Authority said it had flagged risks when Dengvaxia was approved there in October 2016, and was working with Sanofi to strengthen warnings on the drug’s packaging.

According to Sanofi in Manila, 19 licences were granted for Dengvaxia, and it was launched in 11 countries, two of which – the Philippines and Brazil – had public vaccination programmes.

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A spokesman for the Philippines’ president, Rodrigo Duterte, said the government would hold to account those responsible for the programme.

The department of justice on Monday ordered the National Bureau of Investigation to look into “the alleged danger to public health… and if evidence so warrants, to file appropriate charges thereon”.

Former health secretary Janette Garin, who implemented the programme under then-president Benigno Aquino, said she welcomed the investigation: “In the event that there will be authorities who will point culpability to me, I am ready to face the consequences. We implemented it in accordance with WHO guidance and recommendations.”

Presidential spokesman Harry Roque said there had been no reported case of severe dengue infection since the vaccine was administered and urged the public “not to spread information that may cause undue alarm”.