Malaria vaccines protect children, but the protection fades within three years

Two malaria vaccines are now being rolled out to African children, and a systematic review published on 6 September gives the fullest picture yet of what they deliver and where the evidence still thins out [s1]. Following PRISMA methods and registered on PROSPERO (CRD420251032609), the review pooled 56 trials covering 134,424 participants under 18 years, drawing on Phase IIb-IV and post-marketing studies and comparing licensed and candidate vaccines against controls or seasonal malaria chemoprevention (SMC) [s1].

The headline number is modest. Overall vaccine efficacy against clinical malaria was 31%, with an incidence rate ratio of 0.69 (95% CI 0.57-0.84) [s1]. That is meaningful protection against a disease that still kills young children in large numbers, but it is far from the sterilising immunity some early coverage implied.

The two licensed vaccines differ

The pooled figures separate the products. RTS,S/AS01 — the first malaria vaccine to reach children at scale — showed an efficacy of 32% (IRR 0.68, 95% CI 0.57-0.81) [s1]. An older adjuvant formulation, RTS,S/AS02, reached 47% (IRR 0.53, 95% CI 0.36-0.80) [s1]. R21/Matrix-M, the newer and cheaper vaccine now expanding across the continent, showed the highest efficacy in the analysis at 72% (IRR 0.28, 95% CI 0.22-0.34) — but that estimate rests on a single Phase 2b trial, a caveat the authors stress rather than bury [s1].

That single-trial basis matters. A 72% figure from one carefully controlled study is not the same evidence as a 32% figure pooled across many trials and settings, and treating the two as directly comparable would misread the data. The review's own framing is that both licensed vaccines "achieve the highest efficacy particularly in combination with SMC" [s1].

Combining vaccine and chemoprevention

The strongest single result was not a vaccine alone. The combination of vaccination and seasonal malaria chemoprevention showed 65% efficacy (IRR 0.35, 95% CI 0.23-0.51) [s1]. That points to a layered strategy — vaccine plus the antimalarial drug courses already given to children during high-transmission seasons — rather than a choice between the two. It also complicates simple cost comparisons, because the most effective option combines two interventions.

Protection does not last

The clearest warning in the review is about durability. Efficacy fell steadily with time since vaccination: 33% within 12 months (IRR 0.67, 95% CI 0.43-1.02), 35% at 12 to 36 months (IRR 0.65, 95% CI 0.50-0.82), and just 11% beyond 36 months (IRR 0.89, 95% CI 0.81-0.99) [s1]. By three years out, the confidence interval sits close to the line of no effect.

That trajectory is why the authors return repeatedly to boosters. A vaccine whose protection has largely dissipated by the fourth year is a tool for narrowing a window of highest risk in early childhood, not a one-off shield. Immunisation schedules and long-term effectiveness monitoring in endemic settings, they argue, have to be built around that reality [s1].

Safety looks reassuring

On safety, the pooled picture was favourable. The overall serious adverse event rate across trials was 16% (95% CI 12%-19%), reflecting the high background burden of illness in these populations rather than vaccine harm [s1]. It ran higher for RTS,S/AS02 at 29% (95% CI 14%-44%) and markedly lower for R21/Matrix-M at 3% (95% CI 2%-3%) [s1]. Crucially, vaccination reduced the risk of a serious adverse event by 9% compared with controls (RR 0.91, 95% CI 0.86-0.96) — that is, vaccinated children were less likely, not more, to experience a serious event [s1]. Cumulative seroconversion was near-complete at 0.99 (95% CI 0.98-1.00), confirming the vaccines reliably provoke an immune response even where they do not fully prevent disease [s1]. No included study was rated low quality on the RoB2 tool [s1].

What it changes

The review's conclusion is deliberately unglamorous: malaria vaccines "provide meaningful although time-limited protection" and "should be integrated into childhood malaria control strategies emphasizing the need for booster strategies" [s1]. That is a case for using the vaccines widely while keeping expectations calibrated — and for not letting the arrival of a vaccine crowd out bed nets, chemoprevention, and case management.

The gap between a 72% single-trial figure and a 31% pooled figure is the kind of thing that shapes financing decisions and parental confidence alike. The honest reading is that these vaccines work, that R21 in particular looks promising but rests on thinner evidence than headline percentages suggest, and that the protection they buy is real but rented — strongest in the first year or two, and needing reinforcement to hold. For programmes deciding how to spend constrained malaria budgets, the finding that vaccine-plus-chemoprevention outperforms either alone is arguably the most actionable number in the paper [s1].

Sources

• Clinical efficacy, immunogenicity and safety of RTS,S/AS01, R21/Matrix-M and candidate malaria vaccines in children: A systematic review and meta-analysis — Journal of Infection and Public Health, 2026-09-06