#PfSPZ #Vaccination #Malaria #Immunogenicity
In 2023, malaria affected more than 263 million
people worldwide and caused nearly 600,000 deaths, according to the WHO. These
alarming numbers have remained almost unchanged over the past decade,
illustrating the stagnation of global efforts to eliminate this parasitic
disease, despite massive investments. While the development of malaria vaccines
marks undeniable scientific progress, their impact remains largely
insufficient. For instance, the RTS,S/AS01 and R21/Matrix-M vaccines, although
effective against severe forms in young children, have limitations: their
protection against infection is low, it wanes quickly, requires multiple doses,
and shows little efficacy in adults. These shortcomings significantly limit
their potential in eradication strategies and highlight the need for more
effective solutions.
Against this backdrop, the WHO has recently
raised its standards, calling for the development of vaccines capable of
achieving at least 90% efficacy. The goal is clear: to
target all age groups
and strengthen mass vaccination campaigns towards elimination.
It is within this demanding context that the
PfSPZ Vaccine has attracted increasing attention. Developed from
live, but
irradiated, sporozoites to block replication, this vaccine uses a radically
different approach from conventional recombinant protein-based vaccines. By
including thousands of parasite antigens, PfSPZ could offer
broader and
longer-lasting protection, including against genetically diverse strains.
Multiple clinical trials conducted in Africa and Europe have already shown its
ability to induce sterile immunity, notably in naïve or semi-immune adults. The
current challenge is to
validate this efficacy in a simplified format, better
suited to the operational constraints of endemic areas.
Are two doses enough?
The USSPZV7 trial was conducted among
31 adults
who had never been exposed to malaria to evaluate a
condensed vaccination
schedule of the PfSPZ vaccine. This protocol included
two doses administered
one week apart (Day 1 and Day 8), followed by a booster on Day 29.
Immunologically, the results show a
significantly consistent response. Ninety-six percent of participants produced
IgG and IgM antibodies targeting the circumsporozoite protein of Plasmodium
falciparum, with IgG levels rising 99-fold and IgM levels increasing
1,110-fold just one week after the second dose.
The vaccine also demonstrated a
good safety
profile. No serious adverse events were observed. Reported
side effects were
moderate, transient, and typically consisted of fatigue, subjective fever, or
muscle aches, all resolving spontaneously in less than 24 hours.
The frequency
of these effects did not exceed that observed in the placebo group, supporting
the safety of the vaccine under an intensified administration schedule. Most of
these effects occurred
after the second dose, a phenomenon already documented
in other studies with closely spaced multi-dose protocols. However,
no
statistically significant correlation was established between these reactions
and the intensity of the immune response. Reactogenicity therefore is not a
reliable indicator of immunological efficacy.
Read next: Vaccine vs. SMC: rivals or partners?
Fast vaccination, effective vaccination?
Malaria, a mosquito-borne parasitic disease,
remains one of the leading causes of morbidity and mortality in many tropical
regions. Despite current tools for prevention and treatment, progress in
reducing incidence has stalled.
The challenge is therefore twofold: developing
vaccines that are more effective than those already available, while proposing
administration strategies that are simple, rapid, and adapted to high-risk
contexts.
The USSPZV7 study aimed to
assess the safety,
tolerability, and immunogenicity of a condensed PfSPZ vaccine schedule,
administered via direct intravenous injection according to an accelerated
protocol. Results from the first two doses are encouraging. The vaccine is
well
tolerated, with no serious side effects, and induces a
robust immune response
in participants.
The
demonstrated safety profile and
immunogenicity position the PfSPZ Vaccine as a
promising option, especially for
travelers or in the context of targeted elimination campaigns. Its suitability
for short-term scheduling could facilitate operational deployment in settings
with logistical constraints. The next step will be to test this protocol in
larger trials, including more diverse populations—particularly children—and in
endemic areas.
If its clinical efficacy is confirmed, this accelerated
immunization strategy could mark a decisive turning point in the global fight
against malaria. Read next: The mechanisms behind neuromalaria
