The
RTS,S/AS01E vaccine has shown consistent but partial
vaccine efficacy in a pediatric phase 3 clinical trial using a 3-dose immunization schedule. A fourth-dose 18 months after the primary vaccination was shown to restore the waning efficacy. However, only total
IgG against the immunodominant
malaria vaccine epitope has been analyzed following the booster. To better characterize the magnitude, nature, and longevity of the immune response to the booster, we measured levels of total
IgM,
IgG, and IgG1-4 subclasses against three constructs of the circumsporozoite
protein (CSP) and the
hepatitis B surface antigen (
HBsAg, also present in RTS,S) by quantitative
suspension array technology in 50 subjects in the phase 3 trial in Manhiça, Mozambique. To explore the impact of vaccination on naturally acquired immune responses, we measured
antibodies to P. falciparum
antigens not included in RTS,S. We found increased
IgG,
IgG1,
IgG3 and
IgG4, but not
IgG2 nor
IgM, levels against
vaccine antigens 1 month after the fourth dose. Overall, antibody responses to the booster dose were lower than the initial peak response to primary immunization and children had higher
IgG and
IgG1 levels than infants. Higher anti-Rh5
IgG and IgG1-4 levels were detected after the booster dose, suggesting that RTS,S partial protection could increase some blood stage antibody responses. Our work shows that the response to the
RTS,S/AS01E booster dose is different from the primary
vaccine immune response and highlights the dynamic changes in subclass antibody patterns upon the
vaccine booster and with acquisition of adaptive immunity to
malaria.