Sanofi’s dengue vaccine candidate protects more than two-thirds of children aged 9 and older, but could increase the risk of hospitalisation in younger children, according to a new analysis.

The analysis, published in the New England Journal of Medicine, pooled data from two Phase III trials and one Phase IIb trial and found that the vaccine protected 66% of individuals aged 9 and older. It provided even greater protection against severe dengue (93%) and hospitalisation due to dengue (80%).

Sanofi says that this means the vaccine has the potential to “significantly reduce disease burden in endemic countries”.

Maria Rosario Capeding, one of the lead authors of the NEJM article, explains why this age group could be key to this:

"This large, at-risk population includes the most dynamic members of the community who have the potential to spread disease widely and also contribute most to dengue's heavy societal impact in terms of school absences and lost work productivity.”

Risks in younger children

However, the analysis also found that there could be an increased risk of hospitalisation among children younger than 9 who received the vaccine, particularly those aged 2-5.

In an editorial accompanying the NEJM article, Cameron Simmons, a dengue virus researcher at the University of Oxford, says that the vaccine “walks a tightrope” but that the increases in hospitalisation in young children could be a chance finding.

He adds: “A critical question is whether the elevated risk of hospitalisation for dengue that was observed in young recipients is a short-term or long-term phenomenon; potentially, booster doses of vaccine might be used to break the disease-risk profile.”

Sanofi says there is a need for more long-term surveillance to assess the impact of the candidate in this age group.

Dengue is endemic in over 100 countries where almost half the world's population resides – particularly in Asia and Latin America – but there is no specific treatment or prevention available. Sanofi’s vaccine is currently the most advanced inoculation candidate.