Image: Burnet Institute Senior Research Officer Dr Philippe Boeuf

Burnet Institute research has found that immunity to malaria may be better maintained than expected, despite a general decline in immune response associated with a decrease in malaria prevalence globally over recent years.

Published in The Journal of Infectious Diseases, the collaborative study has important implications for malaria surveillance and control measures, and for the development of an effective, long-lasting vaccine.

It investigated the impact of declining malaria transmission on the maintenance of antibodies to Plasmodium falciparum, including functional immunity.

The study quantified the antibody responses to infected red blood cells and two merozoite antigens, AMA1 and MSP2, in blood samples taken from 300 children in Kenya over a three-year period during which malaria transmission markedly declined.

It found that while the levels of antibodies declined as transmission declined, almost three-quarters of the children remained seropositive to AMA1, and more than half the children to MSP2.

In assessing functional immunity, antibodies that fix complement to merozoites did not decline at all, and antibodies promoting opsonic phagocytosis of merozoites declined rapidly.

While there was a wide variation in the retention of antibody levels and function among individuals, contributing author Dr Philippe Boeuf believes that understanding this variability will help to inform vaccine design.

“The study was important because it showed that immunity doesn’t drop as quickly as people thought, and that has implications for understanding people’s risk of malaria epidemics,” Dr Boeuf, Burnet Institute Senior Research Officer, said.

“We found that certain elements of immunity may persist for extended periods of time once malaria transmission has declined, and that they probably provide some level of protection to those people living in regions where malaria is declining.

“The vaccine that we have at the moment is very short-lived in terms of protection. If we can understand why certain people better maintain antibody levels and function than others we can try to mimic this through a vaccine and achieve longer-lasting protection.”

Dr Boeuf said the study could also help to inform the development of a biomarker for recent exposure to malaria. This would allow for the identification of regions with ongoing malaria transmission towards which control efforts should be directed.