Manufacturers of the Dengue vaccine have warned that it may cause serious side effects in patients who have never been infected with the virus. The study released by Sanofi Pasteur, the pharmaceutical company that produce the vaccines, has caused the long term immunisation project in the Philippines to be suspended until further investigations have taken place.

The WHO first recommended in 2016 that Dengvaxia should be given to all those over the age of nine and living in high risk areas. It was estimated that 90% had already been in contact with the virus. The WHO also suggested that it should be used cautiously, and that “vaccination may be ineffective or may theoretically even increase the future risk of (hospitalization) or severe dengue illness in those who are (uninfected) at the time of first vaccination.”

Dengue is a viral infection transmitted by mosquitoes, and the WHO estimates that around half of the world’s population is at risk of contracting the virus. Over 390 million people are infected each year, and of those only a quarter show any symptoms. Symptoms usually include fever, eye pain and muscle pain, but in extreme cases it can cause fatal side effects like internal bleeding and circulatory failure.

Sanofi said in a statement “The analysis confirmed that Dengvaxia provides persistent (protective) benefit against dengue fever in those who had prior infection. For those not previously infected by dengue virus, however, the analysis found that in the longer term, more cases of severe disease could occur following vaccination upon a subsequent dengue infection” and that they would “continue to seek constructive and transparent dialogue” with the Food and Drug Administration of the Philippines.

Harry Roque Jr., a spokesman for Philippines President Rodrigo Duterte, announced that an investigation would be carried out into the safety of Dengvaxia, and that they would work closely with the Department of Health and the Department of Education to monitor all patients who are vaccinated. He said “We will leave no stone unturned in making those responsible for this shameless public health scam which puts hundreds of thousands of young lives at risk accountable.”

According to the WHO, there are four “distinct, but closely related” strains of the virus. Once someone has been infected, they cannot contract the same strain again, but if they subsequently become infected with a different strain this can result in severe symptoms that require immediate medical attention.

A review of Dengvaxia is currently being carried out in the Philippines to assess its safety, and the immunisation project has been put on hold. Sanofi has propose that a “label update” could be used as a temporary measure, and it recommends that medical professionals should be warned not offer the vaccine to patients who’ve been infected with any strain of the virus.

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