  The advancement in the healthcare sector is entering into a new era in the
form of Health 4.0. The integration of innovative technologies like
Cyber-Physical Systems (CPS), Big Data, Cloud Computing, Machine Learning, and
Blockchain with Healthcare services has led to improved performance and
efficiency through data-based learning and interconnection of systems. On the
other hand, it has also increased complexities and has brought its own share of
vulnerabilities due to the heavy influx, sharing, and storage of healthcare
data. The protection of the same from cyber-attacks along with privacy
preservation through authenticated access is one of the significant challenges
for the healthcare sector. For this purpose, the use of blockchain-based
networks can lead to a considerable reduction in the vulnerabilities of the
healthcare systems and secure their data. This chapter explores blockchain's
role in strengthening healthcare data security by answering the questions
related to what data use, when we need, why we need, who needs, and how
state-of-the-art techniques use blockchains to secure healthcare data. As a
case study, we also explore and analyze the state-of-the-art implementations
for blockchain in healthcare data security for the COVID-19 pandemic. In order
to provide a path to future research directions, we identify and discuss the
technical limitations and regulatory challenges associated with
blockchain-based healthcare data security implementation.
