The Strategic Advisory Group of Experts has revised its guidelines for the use of CYD-TDV (Dengvaxia) vaccine, the frst dengue vaccine currently licensed in twenty countries, a WHO report on April 21 said.

The key findings from two large Phase 3 trials involving over 30,000 participants aged 2 to 16 years included: Vaccine efficacy against virologically confirmed dengue, over a 25-month period from the first dose of a three-dose immunization regimen among 9-16 year olds was 65.6 per cent and in this age-group, vaccination reduced severe dengue by 93 per cent and dengue hospitalizations by 82 per cent. An increased risk of hospitalized dengue was seen in the 2 to 5-year age group in Year 3 of follow-up. At the time of Strategic Advisory Group of Experts (SAGE) April 2016 meeting, this increased risk was not observed in those aged 9 years and above.

Because of the higher efficacy of the vaccine against dengue and the absence of an observed increased risk of hospitalized dengue observed in older children, licensure of the vaccine was sought in 2015 with an indication of 9 years and above.
Mathematical modelling suggested that the public health benefits of vaccination could be maximized if dengue seropositivity in the age group targeted for vaccination was high.

WHO issued its position on the use of CYD-TDV in July 2016 based on recommendations provided by SAGE in April 2016, principally, that countries interested in introducing the vaccine consider its use only in those aged 9 years and above, and in areas with a seroprevalence of ≥70 per cent, and not in areas below 50 per cent. SAGE noted that the evidence of the absence of a safety issue in seronegative individuals aged 9 and above was based on the limited data set of 10-20 per cent of the trial population, and highlighted the urgent need to better describe the long-term benefit-risk ratio of CYD-TDV in seronegative individuals.