Maternal Antibodies May Interfere with Malaria Vaccine Responses: Study Finds - Video

Maternal antibodies passed across the placenta can interfere with the response to the malaria vaccine, which would explain its lower efficacy in infants under five months of age, according to research led by the Barcelona Institute for Global Health (ISGlobal), in collaboration with seven African centers. The findings, published in Lancet Infectious Diseases, suggest that children younger than currently recommended by the WHO may benefit from the RTS,S and R21 malaria vaccines if they live in areas with low malaria transmission, where mothers have less antibodies to the parasite.

“We know that the RTS,S/AS01E malaria vaccine is less effective in infants under five months of age, but the reason for this difference is still debated,” says Carlota Dobaño, who leads the Malaria Immunology group at Barcelona Institute for Global Health, a centre supported by “la Caixa” Foundation.

To investigate this, Dobaño and her team analysed blood samples from more than 600 children (age 5-17 months) and infants (age 6-12 weeks) who participated in the phase 3 clinical trial of RTS,S/AS01E. Using protein microarrays, they measured antibodies against 1,000 P. falciparum antigens before vaccination to determine if and how malaria exposure and age affected IgG antibody responses to the malaria vaccine.

The analysis of antibodies to P. falciparum in children who had received a control vaccine instead of RTS,S/AS01E revealed a typical “exposure” signature, with high levels in the first three months of life due to the passive transfer of maternal antibodies through the placenta, a decline during the first year of life, and then a gradual increase as a result of naturally acquired infections.

In children vaccinated with RTS,S/AS01E, antibodies induced by natural infections did not affect the vaccine response. However, in infants, high levels of antibodies to P. falciparum, presumably passed from their mothers during pregnancy, correlated with reduced vaccine responses. The higher the level of malaria transmission, the more maternal antibodies are transmitted to the baby, resulting in lower vaccine effectiveness.

Reference: The effect of Plasmodium falciparum exposure and maternal anti-circumsporozoite protein antibodies on responses to RTS,S/AS01E vaccination in infants and children: an ancillary observational immunological study to a phase 3, randomised clinical trial. Macià, Dídac et al.The Lancet Infectious Diseases, Volume 0, Issue 0