New dengue vaccine may up infection in low affected areas: study

London : The newly licensed dengue vaccine may actually increase the incidence of infections if used in low transmission areas, a team of international researchers has warned.

Dengue a viral infection that records nearly 400 million cases per year is spread by mosquitoes, and causes fever, headache, muscle and joint pain.

The virus typically causes a mild first infection but a far worse one if someone is infected with the disease a second time, researchers said.

The study found that the dengue vaccine with the trade name Dengvaxia can reduce illness and hospitalisation by 20 to 30 per cent in places where there is high transmission of dengue.

"If someone has never been exposed to dengue, the vaccine seems to act like a silent infection. The initial exposure to the virus from the vaccine primes the immune system, so when they are infected again, the symptoms are more likely to be severe," said Neil Ferguson, Professor at Imperial College London.

On the other hand, it may significantly increase illness and hospitalisation if used in locations where there is lower transmission of the virus.

"In places with high transmission intensity, most people have been already exposed to dengue at the time of vaccination, and the vaccine has higher efficacy on average," added Derek Cummings, Professor at the University of Florida, US.

"However, in places with lower transmission intensity, were individuals haven't been previously exposed, the vaccine can place people at risk of severe disease and overall, increase the number of hospitalized cases," Cummings noted.

Importantly, the vaccine cannot be used for children under the age of nine, the researchers said.