The vaccine against malaria is closer to becoming a reality. A few days ago, a clinical trial was published in the journal Withwhere they ensure that the vaccine appears safe and favors the immune response in African infants, one of the most vulnerable groups to severe malaria.
Currently, there is only one vaccine against malaria, RTS,S, approved by the World Health Organization and offers partial protection against disease. However, results from a Phase Ib trial in Tanzania have found that targeting RH5 — a protein that the malaria pathogen Plasmodium falciparum uses to invade red blood cells — can generate a promising immune response that it is more pronounced in a cohort of infants.
“For prevent disease, antisporozoite vaccines such as RTS,S should be 100% effective in preventing the parasite from invading the liver,” explains Angela Minassian, lead author and clinical scientist at the University of Oxford, UK.
“Although a single parasite sneaks into the net, it will multiply in the liver, it will pass into the bloodstream and infect red blood cells, where it will grow at an exponential rate,” he continues. Having a blood phase vaccine like RH5 provides a second line of defense once the parasite has entered the bloodstream, allowing a second chance to stop malaria before it causes disease.”
A person becomes infected with malaria when they are bitten by an infected mosquito, which releases ‘Plasmodium falciparum’ into the body. RTS,S and many other candidate vaccines teach the immune system to attack the parasite at this sporozoite stage, before it invades the liver.
Once the parasite matures and is released from the liver into the bloodstream, Plasmodium falciparum unfolds RH5 and infects red blood cells, causing the disease. If a combined anti-sporozoite and anti-RH5 vaccine were used in the future, individuals could experience more effective protection against malaria over a longer period of time.
“Data from the phase 1b trial reported here confirm, for the first time, that substantial anti-RH5 immune responses can be safely achieved by vaccination in infants from an area where malaria is endemic,” the authors state.
The researchers conducted the vaccine trial in Bagamoyo, Tanzania, where the average prevalence of malaria in the entire population is 13%. they signed up 63 participants aged between 6 months and 35 yearswho were randomly assigned to receive the experimental malaria vaccine, called ‘ChAd63-MVA RH5’, or a control rabies vaccine.
The trial was also double-blind, which means that neither the participants nor the vaccine administrators knew who was receiving the malaria vaccine or the control. All participants received the second dose of the vaccine two months later and were followed for a further four months.
The main objective of this study was to evaluate the safety of this vaccine in a population where malaria is endemic. Participants in both the control and treatment groups reported pain at the injection site and mild fever shortly after vaccination, but the vaccine was generally well tolerated and there were no safety concerns.
A secondary outcome of the study was whether the vaccine would promote an immune response. The researchers found that participants who received the malaria vaccine developed antibodies against RH5 in their blood during follow-up.
At the laboratory, these antibodies were able to inhibit the growth of the malaria parasite at elevated levels that are associated with protection against disease.
“These data justify the move to Phase IIb field efficacy trials to determine if some levels of inhibition of parasite growth of this magnitude may ultimately protect against clinical malaria,” they say.
The authors point out that they observed the stronger immune responses in infants younger than 11 months, followed by children 1 to 6 years, and then adults.
“It remains to be understood why infants and young children vaccinated with ChAd63-MVA RH5 induced such high levels of antibodies,” they point out. “Since vaccination strategies against the sporozoite and against the hematopoietic stage of malaria require very high levels of antibodies to protect against parasitic infection, current efforts remain focused on infants and young children“.
The researchers note that this is a small study in which a follow-up of the participants for only four months after receiving the full vaccination schedule. They recommend that additional phase Ia/Ib trials be conducted to optimize the recommended age range, booster schedule, and delivery platform of the anti-RH5 vaccines.
At present, it is planned to carry out a phase 1b trial in The Gambia in which the effects of the combination of anti-RH5 and anti-RH5 vaccines will be studied.
2023-08-27 03:00:00
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