Duration of protection with RTS,S/AS02A malaria vaccine in prevention of Plasmodium falciparum disease in Mozambican children: single-blind extended follow-up of a randomised controlled trial.

BACKGROUND: RTS,S/AS02A is a pre-erythrocytic stage malaria vaccine that provides partial protection against infection in malaria-naive adult volunteers and hyperimmune adults. A previous report showed that this vaccine reduced risk of clinical malaria, delayed time to new infection, and reduced episodes of severe malaria over 6 months in African children. An important remaining issue is the durability of protection against clinical disease in these children. METHODS: We did a randomised, controlled, phase IIb trial of RTS,S/AS02A given at 0, 1, and 2 months in 2022 Mozambican children aged 1-4 years. We previously determined vaccine efficacy (VE) against clinical malaria in a double-blind phase that included study months 2.5-8.5 (VE(2.5-8.5)). We now report VE in a single-blind phase up to month 21 (VE(8.5-21)). The primary endpoint was time to first or only clinical episode of Plasmodium falciparum malaria (axillary temperature 37.5 degrees C and P falciparum asexual parasitaemia >2500 per microL) detected through a passive case detection system. We also determined VE for other case definitions and for episodes of severe malaria. This study is registered with the ClinicalTrials.gov identifier NCT00197041. FINDINGS: During the single-blind phase, VE(8.5-21) was 28.9% (95% CI 8.4-44.8; p=0.008). At month 21, prevalence of P falciparum infection was 29% lower in the RTS,S/AS02A group than in the control (p=0.017). Considering the entire study period, VE(2.5-21) was 35.3% (95% CI 21.6-46.6; p<0.0001) and VE(2.5-21) for severe malaria was 48.6% (95% CI 12.3-71.0; p=0.02). INTERPRETATION: These results show that RTS,S/AS02A confers partial protection in African children aged 1-4 years living in rural endemic areas against a range of clinical disease caused by P falciparum for at least 18 months, and confirm the potential of malaria vaccines to become credible control tools for public-health use.

Efficacy of the RTS,S/AS02A vaccine against Plasmodium falciparum infection and disease in young African children: randomised controlled trial.

BACKGROUND: Development of an effective malaria vaccine could greatly contribute to disease control. RTS,S/AS02A is a pre-erythrocytic vaccine candidate based on Plasmodium falciparum circumsporozoite surface antigen. We aimed to assess vaccine efficacy, immunogenicity, and safety in young African children. METHODS: We did a double-blind, phase IIb, randomised controlled trial in Mozambique in 2022 children aged 1-4 years. The study included two cohorts of children living in two separate areas which underwent different follow-up schemes. Participants were randomly allocated three doses of either RTS,S/AS02A candidate malaria vaccine or control vaccines. The primary endpoint, determined in cohort 1 (n=1605), was time to first clinical episode of P falciparum malaria (axillary temperature > or =37.5 degrees C and P falciparum asexual parasitaemia >2500 per microL) over a 6-month surveillance period. Efficacy for prevention of new infections was determined in cohort 2 (n=417). Analysis was per protocol. FINDINGS: 115 children in cohort 1 and 50 in cohort 2 did not receive all three doses and were excluded from the per-protocol analysis. Vaccine efficacy for the first clinical episodes was 29.9% (95% CI 11.0-44.8; p=0.004). At the end of the 6-month observation period, prevalence of P falciparum infection was 37% lower in the RTS,S/AS02A group compared with the control group (11.9% vs 18.9%; p=0.0003). Vaccine efficacy for severe malaria was 57.7% (95% CI 16.2-80.6; p=0.019). In cohort 2, vaccine efficacy for extending time to first infection was 45.0% (31.4-55.9; p<0.0001). INTERPRETATION: The RTS,S/AS02A vaccine was safe, well tolerated, and immunogenic. Our results show development of an effective vaccine against malaria is feasible.

Safety of the RTS,S/AS02A malaria vaccine in Mozambican children during a Phase IIb trial.

RTS,S/AS02A is a pre-erythrocytic vaccine candidate based on the Plasmodium falciparum circumsporozoite surface antigen and is currently the most advanced malaria vaccine candidate in development. A proof of concept phase IIb trial of the RTS,S/AS02A in Mozambican children aged 1-4 years determined a vaccine efficacy against risk of clinical malaria of 35.3% (95% CI 21.6-46.6; p<0.0001) and against severe malaria of 48.6% (95% CI 12.3-71.0; p=0.02). We evaluated the safety of the RTS,S/AS02A vaccine. 2022 children that received at least one vaccine dose of RTS,S/AS02A or control vaccines were included in the intention to treat safety analysis. Vaccine safety was evaluated using active and passive follow-up. Participants were observed for at least 1h after each dose. Trained field workers visited children at home daily for the next 3 days to record solicited and unsolicited local and general symptoms. Investigators followed-up participants with severe adverse events until month 21. Overall, we recorded 1712 unsolicited adverse events after vaccination, 53% in the intervention and 47% in the control group. Most unsolicited adverse events reported with RTS,S/AS02A were self-limited, and participants recovered without sequelae. Local reactogenicity increased with the number of doses. The proportion of children experiencing serious adverse events was lower in the RTS,S/AS02A recipients compared to the control group (Engerix-Btrade mark or Prevnartrade mark and Hiberixtrade mark). Overall, these results indicate that the RTS,S/AS02A vaccine has a good safety profile and well tolerated when given in three doses to semi-immune children living in malaria-endemic areas.

Safety of the RTS, S/AS02A malaria vaccine in Mozambican children during a Phase IIb trial / Safety of the RTS,S/AS02A malaria vaccine in Mozambican children during a Phase IIb trial

RTS,S/AS02A is a pre-erythrocytic vaccine candidate based on the Plasmodium falciparum circumsporozoite surface antigen and is currently the most advanced malaria vaccine candidate in development. A proof of concept phase IIb trial of the RTS,S/AS02A in Mozambican children aged 1-4 years determined a vaccine efficacy against risk of clinical malaria of 35.3% (95% CI 21.6-46.6; p<0.0001) and against severe malaria of 48.6% (95% CI 12.3-71.0; p=0.02). We evaluated the safety of the RTS,S/AS02A vaccine. 2022 children that received at least one vaccine dose of RTS,S/AS02A or control vaccines were included in the intention to treat safety analysis. Vaccine safety was evaluated using active and passive follow-up. Participants were observed for at least 1h after each dose. Trained field workers visited children at home daily for the next 3 days to record solicited and unsolicited local and general symptoms. Investigators followed-up participants with severe adverse events until month 21. Overall, we recorded 1712 unsolicited adverse events after vaccination, 53% in the intervention and 47% in the control group...

Efficacy of the RTS, S/AS02A vaccine against Plasmodium falciparum infection and disease in young African children: randomised controlled trial

Background: Development of an effective malaria vaccine could greatly contribute to disease control. RTS,S/AS02A is a pre-erythrocytic vaccine candidate based on Plasmodium falciparum circumsporozoite surface antigen. We aimed to assess vaccine efficacy, immunogenicity, and safety in young African children. Methods: We did a double-blind, phase IIb, randomised controlled trial in Mozambique in 2022 children aged 1-4 years. The study included two cohorts of children living in two separate areas which underwent different follow-up schemes. Participants were randomly allocated three doses of either RTS,S/AS02A candidate malaria vaccine or control vaccines. The primary endpoint, determined in cohort 1 (n=1605), was time to first clinical episode of P falciparum malaria (axillary temperature > or =37.5 degrees C and P falciparum asexual parasitaemia >2500 per microL) over a 6-month surveillance period. Efficacy for prevention of new infections was determined in cohort 2 (n=417). Analysis was per protocol. Findings: 115 children in cohort 1 and 50 in cohort 2 did not receive all three doses and were excluded from the per-protocol analysis. Vaccine efficacy for the first clinical episodes was 29.9% (95% CI 11.0-44.8; p=0.004). At the end of the 6-month observation period, prevalence of P falciparum infection was 37% lower in the RTS,S/AS02A group compared with the control group (11.9% vs 18.9%; p=0.0003). Vaccine efficacy for severe malaria was 57.7% (95% CI 16.2-80.6; p=0.019). In cohort 2, vaccine efficacy for extending time to first infection was 45.0% (31.4-55.9; p<0.0001). Interpretation: The RTS,S/AS02A vaccine was safe, well tolerated, and immunogenic. Our results show development of an effective vaccine against malaria is feasible