Introduction and Significance

Developed collaboratively by the University of Oxford and the Serum Institute of India (SII) utilizing Novavax's Matrix-M adjuvant.
Represents the second malaria vaccine to achieve World Health Organization (WHO) prequalification in December 2023.
Designed specifically to target Plasmodium falciparum, the pathogen responsible for severe neurological complications, severe anemia, and high mortality in children under five years of age.

Composition and Mechanism of Action

Composed of a recombinant virus-like particle (VLP) that displays the circumsporozoite protein (CSP).
Features a structurally optimized antigen-to-scaffold ratio, providing a higher density of CSP antigens compared to the first-generation RTS,S/AS01 vaccine.
Incorporates the Matrix-M saponin-based adjuvant to stimulate potent humoral and cell-mediated (T-cell) immune responses.
Functions by inducing neutralizing antibodies that bind to sporozoites immediately following an infectious anopheline mosquito bite, effectively blocking entry into hepatic parenchymal cells and arresting the parasite's life cycle.

Parameter	Clinical Guidelines
Target Demographic	Infants and children aged 5 to 36 months residing in areas with moderate-to-high malaria transmission.
Primary Series	3 doses administered intramuscularly (0.5 mL) at 4-week intervals.
Initiation Age	Standard initiation occurs at 5 months of age alongside routine Expanded Programme on Immunization (EPI) vaccines.
Booster Dose	A mandatory 4th dose administered 12 months after the 3rd dose to restore declining antibody titers.

Phase III clinical trials proved high efficacy, meeting the WHO goal of $\ge 75\%$ protection against clinical malaria.
Demonstrates 75% efficacy in seasonal transmission regions and 67-68% efficacy in perennial transmission zones.
Formulated with a low antigen dose (5 μg), enabling high-volume manufacturing scalability and reducing procurement costs.
National rollouts utilize two strategic delivery models based on epidemiology:
- Perennial Model: Age-based delivery seamlessly integrated into routine infant immunization schedules for areas with year-round transmission.
- Seasonal Model: Mass campaigns timed so the 3rd primary dose and the booster dose are administered immediately prior to the onset of the peak high-transmission rainy season.

Maintains thermal stability within a standard cold chain of $2^\circ\text{C}$ to $8^\circ\text{C}$, circumventing the need for ultra-low temperature storage.
The Indian Academy of Pediatrics (IAP) ACVIP 2025 schedule recommends considering the R21 vaccine for children traveling to endemic areas and residents living in remaining high-transmission pockets.
Public health implementation must include caregiver counseling to ensure the vaccine is used as a complementary tool alongside insecticide-treated bed nets (ITNs) and indoor residual spraying (IRS) rather than a standalone replacement.

Exhibits an excellent safety profile with mild-to-moderate local injection-site reactions (pain, erythema, induration) and transient pyrexia.
Active surveillance demonstrates no increased risk for anaphylaxis, febrile seizures, or complex neurological complications.