Estimated impact of RTS, S / AS01 malaria vaccine allocation strategies in sub-Saharan Africa: a modeling study

Release date: November 30, 2020

https://doi.org/10.1371/journal.pmed.1003377

DESCRIPTION

The background to this study is that the RTS, S / AS01 vaccine against Plasmodium falciparum malaria infection completed a phase III trial in 2014, showing approximately 36% efficacy against clinical malaria over 4 years with a 4-dose schedule in children aged 5-17 months.

Implementation of the pilot vaccine has begun in three African countries.

If the pilot shows a positive health impact and addresses remaining safety concerns, it is hoped that a broader rollout may be recommended after 2021, but demand for the vaccine may exceed the initial supply.

Therefore, mathematical modeling was used in this study to identify where vaccine deployment should be prioritized to maximize public health impact under different supply constraints.

The study uses a mathematical model of P.

Plasmodium falciparum malaria malaria infections and the impact of RTS, S vaccine, averted clinical cases and deaths in children aged 0-5 years in sub-Saharan Africa were estimated in two scenarios of vaccine coverage and two scenarios of other interventions.

We also used a prioritization algorithm to identify potential allocation efficiency gains from prioritizing vaccine allocations among countries and administrative units to maximize averted cases and deaths.

If the malaria burden at introduction remains similar to current levels, an estimated 4.3 million malaria cases 

For children under 5 years of age, the potential for annual avoidance is considered at a dose constraint of 30 million, decreasing to 3 million cases and 14,000 deaths at a dose constraint of 20 million, and increasing to 6.6 million cases. 

At 100% vaccination coverage, this effect estimate increases to 5.2 million cases and 27,000 deaths, and 3.9 million cases and 19,000 deaths.

Under realistic vaccine coverage, 5.3 million cases and 24,000 deaths could be avoided with a dose constraint of 30 million if the vaccine were prioritized nationally.

In addition, local prioritization would allow introduction in almost twice as many countries as national prioritization.

Prioritizing the introduction of the vaccine in the three pilot countries (Ghana, Kenya, and Malawi) will reduce the health impact, but this impact is not expected to be significant if more than 50 million doses are available.

Because the optimization was based on a single outcome measure, without accounting for national variations in vaccination coverage, the study should be used to understand overall trends rather than to guide country-specific allocations, according to the authors.

This conclusion suggests that the impact of vaccine supply constraints on the public health impact of RTS and S malaria vaccines can be reduced by introducing vaccines at the sub-national level and prioritizing countries with the highest incidence of malaria.