June 8, 2021 – The PfSPZ malaria vaccines of Sanaria Inc. are unique in vaccine development as they are composed of weakened (attenuated) forms of the live parasite cells that cause malaria. These parasite cells are called eukaryotic cells and there are no vaccines against any infectious disease composed of such cells. Furthermore, there are no licensed vaccines against any infectious disease caused by a eukaryotic pathogen. Thus, Sanaria and its collaborators have had to take a step by step empirical approach to optimizing immunization with PfSPZ vaccines to achieve a safe, effective, durable, and broadly protective malaria vaccine.
Two recent landmark malaria vaccine studies have moved the optimization process forward and highlighted the strong protective efficacy of Sanaria® PfSPZ-CVac in malaria-naïve adults. In a study published in Nature Communications, 77% (10/13) of subjects vaccinated with a 3-dose regimen administered within a 4 week period were protected 12 weeks later when challenged with live malaria parasites of a strain genetically quite distant (heterologous) from the vaccine strain.
“This high-level efficacy of 3 months would be excellent for protecting travelers to malaria endemic regions against the disease,” said Professor Peter Kremsner, Director of the Institute of Tropical Medicine, Travel Medicine and Human Parasitology at the University of Tübingen, Germany who led the study. “We have demonstrated excellent efficacy with just three co-administrations of PfSPZ-CVac and chloroquine, paving the way for a product that can be used for travelers worldwide.”
The second study, published in PLoS Pathogen, revealed the profound negative effects of the presence of blood stage malaria parasites on vaccine efficacy. Vaccinations given 7 days apart conferred no protection in study subjects, and this timing coincided with the emergence of parasites into the blood from the liver after previous doses. By changing the timing between doses to 5 days, a regimen first reported in Nature by the Tübingen team, PfSPZ-CVac protective efficacy dramatically increased to 75%. “This study demonstrates the capacity of the malaria parasite to manipulate immune responses of the human host in favor of its own survival and demonstrates how we can optimize the spacing of doses of PfSPZ-CVac to overcome this negative impact,” said Dr. Sean Murphy, first author of the paper and Associate Professor at the Department of Laboratory Medicine and Pathology, University of Washington. “Given the high prevalence of malaria infection, these results also have profound implications for malaria vaccine immunization strategies in Africa.”
Sanaria® PfSPZ-CVac is a chemo-attenuated, live whole parasite vaccine in which an anti-malarial drug is co-administered with the parasite cells (PfSPZ), to kill parasites. Efficacy in these studies was measured by controlled human malaria infection (CHMI) in which well-characterized, infectious malaria parasites were administered to vaccinated subjects. This is a highly rigorous measure of efficacy because a 100% infective dose of disease-causing parasites is administered and the heterologous challenge strain used in Tübingen is genetically more distant from the vaccine strain than parasites encountered naturally in Africa. Additionally, CHMI is not subject to seasonal variations, subject behaviors, or other unknown variables, as is the case in observational field trials.