Blocking human-to-mosquito malaria transmission promises big public health gains

Vaccines that block the transmission of malaria from human to mosquito can lead to great public health gains, particularly when implemented in schoolchildren, a recent modelling study has shown.

In order to translate lab-calculated transmission-blocking activity (TBA) of a vaccine into field-relevant figures, the researchers used naturally infected mosquitoes collected from Burkina Faso, West Africa. A transmission dynamics model was then constructed to estimate the public health impacts of the vaccine.

The model showed that a vaccine with a transmission reduction activity (TRA) of around 90-percent would have an estimated TBA of 83 percent in asymptomatic patients with submicroscopic infections. In those who are asymptomatic but have infections detectable by microscopy, the same vaccine would have a blocking efficacy of 66 percent.

The TBA dropped further in individuals with untreated, symptomatic malaria, yielding an efficacy of 17 percent. Nevertheless, considering the changes in infection states over the year, the researchers suggested that a 90-percent TRA vaccine would have an overall population average efficacy of 72 percent, ranging from 74 percent in the dry season to 70 percent at peak season.

In a hypothetical scenario, where 80 percent of the population is vaccinated at the start of the transmission season, the TBV reduced prevalence by microscopy by around 25 percent. This effect became apparent 4 months after vaccination.

The impact was stronger on the infectious reservoir, with the vaccine reducing the entomological inoculation rate by almost half.

When looking at target groups for vaccination, the researchers found that targeting children around 10 years of age could avert the largest number of cases. In a high-transmission scenario, for example, inoculating 8–10-year-olds could prevent twice as many cases than when targeting those aged 2–4 and 15–18 years.