The third day at the Keystone Symposium on The Science of Malaria Eradication
was an action packed day of exciting discussions on vaccines and tools to measure transmission, with an interlude to the Mayan ruins of Mayapan, where the malaria community rhetorically climbed the 'Mayan pyramids' of eradication.
A passionate Stephen Hoffman (Sanaria, USA) opened the morning session with encouraging results on the safety and efficacy of the irradiated sporozoite vaccine candidate (PfSPZ) and plans for future work. In the context of transmission blocking vaccines (TBV) Patrick Duffy (National Institute of Health, USA) shared the positive outcomes on safety and transmission blocking activity of the vaccine candidate based on the Pfs25 antigen. Other vaccine targets were presented by Veronique Beiss (Fraunhofer Institute, Germany) and Daria Nikolaeva (National Institute of Health, USA) based on sexual-stage proteins. Participants discussed that studying transmission-blocking vaccine targets also helps our understanding of how transmission actually works and could open doors to identifying immunological biomarkers of transmission activity in populations.
In the related field of immunology, Carlota Dobaño
(CRESIB-ISGlobal, Spain) exposed a series of studies currently underway to better characterize the immune responses to the RTS/s vaccine candidate
, and consequently identify surrogates of protection. David Kaslow (Malaria Vaccines Initiative, PATH, USA) finalized the session with a reflection on the regulatory path to licensure of vaccines to interrupt malaria transmisssion (VIMTs) and suggested the direct feeding assay was potentially a critial tool in the regulatory strategy.
After a relaxing lunch and tour to the Mayan ruins, the Symposium continued with a series of presentations on tools to measure parasite transmission intensity
. Rick Steketee (MACEPA, PATH, USA) provided an explanatory summary of the different tools available and their advantages and disadvantages in different transmission settings. He emphasized on the need to constantly update research to inform ongoing elimination programmes. Ivo Mueller
(Walter and Eliza Hall Institute, Australia and CRESIB-ISGlobal, Spain), highlighted the particularities of measuring P. vivax
transmission in low transmission settings. Considerations ranged from asymptomatic individuals, increasingly prevalent sub-microscopical positive samples, and the challenges in the relationship between gametocytemia and infectiousness. Sara Volkman (Harvard School of Public Health, USA), then presented her barcoding tool that takes advantage of the parasite's responses to selective pressure to measure transmission intensity and evaluate the impact of interventions in the context of elimination programmes. Further work will help understand if the barcoding tool will be able to distinguish imported and autochthonous cases. The short talks highighted innovative research in measuring pregnancy-specific proteins as indicators of transmission. Ana Maria Fonseca
(CRESIB-ISGlobal, Spain) shared initial results on the VAR2CSA pregnancy protein as a potential candidate to estimate malaria transmission in the population. Another innovative tool, the magneto-optic detection of parasite haemozin, was presented by David Newman (Exeter University, UK).
The combination of these topics led to a series of discussions ranging from the role of asymptomatic individuals and relapsing cases on transmission; to the need for research to inform target product profiles, such as profiling immunogenicity to help identify new vaccine targets; and the need to better understand the mechanisms of transmission in different human and parasite populations in order to support programs moving towards elimination.