This systematic literature review (SLR) investigates blockchain-enabled vaccine supply chains that leverage real-time Internet of Things (IoT) monitoring, advanced scalability techniques such as sharding and edge computing, and robust privacy-preserving mechanisms. Following a rigorous methodology, we systematically analyzed and classified 40 peer-reviewed studies published from extensive academic databases, focusing on blockchain architecture types, IoT integration methodologies, privacy and security measures, as well as regulatory compliance strategies. Ethereum-based platforms were predominant (15 out of 40 studies) due to their transparency and decentralized governance, whereas permissioned platforms like Hyperledger Fabric (5 studies) offered enhanced access control and compliance capabilities. IoT sensor technologies, often combined with Radio Frequency Identification (RFID), were extensively integrated (in 37 studies) to ensure real-time validation of critical cold-chain conditions. Privacy-preserving approaches identified include encryption, zero-knowledge protocols, and careful on-chain/off-chain data partitioning. Despite these advances, the review highlights a significant lack of standardized performance metrics, underscoring an important gap for future research. This paper synthesizes current trends, identifies technological strengths and limitations, and provides recommendations to guide future blockchain-based vaccine supply chain architectures toward improved scalability,security, and regulatory adherence.