<p>Global health crises and cross-border travel requirements have highlighted the need for vaccine certification systems that are secure, lightweight, and practical across diverse deployment settings. Traditional paper-based certificates are vulnerable to tampering and forgery, while centralized digital solutions may suffer from single points of failure, limited interoperability, and deployment constraints in low-resource environments. In this paper, we present a blockchain-based framework for vaccine certification with emphasis on lightweight user-side operation, QR-based certificate presentation, and implementation feasibility in heterogeneous deployment settings. Unlike smartphone-only approaches, the proposed framework supports both digital and QR-based certificates and provides online verification through blockchain access, together with a bounded offline verification mode based on locally cached trust material, certificate signatures, and freshness assumptions. The framework implements core certification operations, including certificate issuance, certificate verification, and vaccine-lot validation, while limiting direct on-chain exposure of user-related data through hashed and signed records. To support efficient retrieval and verification, we design and implement Ethereum smart contracts with indexing structures for certification data. The evaluation reports prototype-level implementation results in terms of gas consumption and certificate retrieval performance. These results demonstrate the feasibility of the indexing-based smart-contract design under the evaluated setting, while broader claims regarding large-scale deployment, regulatory compliance, biometric robustness, and offline revocation guarantees remain dependent on deployment-specific infrastructure and policies.</p>