The paper by Pastor-Satorras and Vespignani explores the immunization of complex networks, particularly focusing on scale-free networks. They demonstrate that random uniform immunization does not effectively eradicate infections in these networks, even with high densities of immunized individuals. Scale-free networks, characterized by a power-law distribution of node degrees, exhibit unbounded connectivity fluctuations, leading to the absence of a critical immunization threshold. Successful immunization strategies must account for the inhomogeneous connectivity properties of these networks. The authors propose two targeted immunization schemes: proportional immunization, which immunizes nodes based on their connectivity, and targeted immunization, which focuses on the most connected nodes. These schemes significantly reduce the network's vulnerability to epidemic attacks, even with a small fraction of immunized individuals. The study highlights the importance of understanding the unique properties of scale-free networks in designing effective immunization strategies, with potential applications in various fields such as epidemiology, social networks, and technological systems.The paper by Pastor-Satorras and Vespignani explores the immunization of complex networks, particularly focusing on scale-free networks. They demonstrate that random uniform immunization does not effectively eradicate infections in these networks, even with high densities of immunized individuals. Scale-free networks, characterized by a power-law distribution of node degrees, exhibit unbounded connectivity fluctuations, leading to the absence of a critical immunization threshold. Successful immunization strategies must account for the inhomogeneous connectivity properties of these networks. The authors propose two targeted immunization schemes: proportional immunization, which immunizes nodes based on their connectivity, and targeted immunization, which focuses on the most connected nodes. These schemes significantly reduce the network's vulnerability to epidemic attacks, even with a small fraction of immunized individuals. The study highlights the importance of understanding the unique properties of scale-free networks in designing effective immunization strategies, with potential applications in various fields such as epidemiology, social networks, and technological systems.