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Science Notebook

Finally! A safe and effective vaccine against malaria

Published : Jan 26, 2023 10:25 IST

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Finally! A safe and effective vaccine against malaria

A depiction of the life cycle of the malaria parasite showing the various stages relevant to vaccine design. (1) The mosquito vector, used in experimental protocols to immunise people with irradiated sporozoites administered by mosquito bite; (2) the sporozoite, the target of several vaccines; (3) the liver stage, usually targeted by vectored vaccines; (4) the blood stage, usually targeted by the protein in adjuvant vaccine candidates; (5) the gametocyte that along with the ookinete, formed after fertilisation in the mosquito mid-gut, is the source of parasite antigens used in sexual-stage transmission-blocking vaccines. Pre-erythrocytic vaccines, which target the sporozoite and the liver-stage parasite, are intended to prevent infection and disease while blood-stage vaccines are intended to prevent clinical illness and death.

A depiction of the life cycle of the malaria parasite showing the various stages relevant to vaccine design. (1) The mosquito vector, used in experimental protocols to immunise people with irradiated sporozoites administered by mosquito bite; (2) the sporozoite, the target of several vaccines; (3) the liver stage, usually targeted by vectored vaccines; (4) the blood stage, usually targeted by the protein in adjuvant vaccine candidates; (5) the gametocyte that along with the ookinete, formed after fertilisation in the mosquito mid-gut, is the source of parasite antigens used in sexual-stage transmission-blocking vaccines. Pre-erythrocytic vaccines, which target the sporozoite and the liver-stage parasite, are intended to prevent infection and disease while blood-stage vaccines are intended to prevent clinical illness and death. | Photo Credit: Philosophical Transactions of the Royal Society

In African adults who previously had malaria, PfSPZ provided 52 per cent efficacy.

FOR decades scientists had tried different approaches to develop an effective malaria vaccine without much success. Researchers at the Center for Vaccine Development and Global Health (CVD) of the University of Maryland School of Medicine (UMSOM) recently demonstrated that a three-dose regimen of a vaccine called Plasmodium falciparum sporozoite (PfSPZ) was safe and efficacious when tested in adults living in Burkina Faso, West Africa, where malaria is endemic. This finding was published in a recent issue of Science Translational Medicine.

PfSPZ Vaccine, made by the Rockville, Maryland-based Sanaria Inc., has a live-attenuated form of the malaria parasite P. falciparum sporozoite and was shown to provide at least 90 per cent protection in challenge studies where volunteers were infected with malaria (in a highly controlled way).

Matthew B. Laurens, a professor of paediatrics at the UMSOM and head of the CVD’s malaria research group, said: “Our study shows that the vaccine can be given to malaria-experienced adults in a highly endemic area and still provide protection, which is difficult and complicated as these individuals already have significant immune responses to malaria parasites that must be overcome by a vaccine for it to be successful.”

The two-part study was conducted in the US,Tanzania, and Burkina Faso. The first part was in the US and Tanzania in 2016 and enrolled 32 adults in a dose-escalation phase. The second part was in Burkina Faso in 2017 and enrolled 80 adults in a randomised trial in which 39 received PfSPZ Vaccine (a 10-fold higher dose than was used in the first part) and 41 the placebo. Study participants were healthy men and non-pregnant women aged from 21 to 40. The vaccines were well tolerated and without concerning side effects according to the UMSOM release. In African adults who previously had malaria, PfSPZ provided 52 per cent efficacy against naturally transmitted malaria infection. Protection lasted eight to 14 months.

(This story was published in the print edition of Frontline magazine dated Feb 10, 2023.)

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