<p>Measles remains a major global public health challenge despite available vaccines. To evaluate the combined impact of routine immunization and supplementary vaccination campaigns, we developed a compartmental mathematical model that incorporates declining immunity and breakthrough infections. We derived the control reproduction number using the next-generation matrix method, analyzed stability and bifurcation properties of the equilibria, and conducted sensitivity analysis to determine key drivers of transmission. The model was parameterized from the literature and calibrated to 2024 Nigerian measles case data using Markov Chain Monte Carlo sampling. The model revealed that the disease-free equilibrium is globally stable when the control reproduction number is less than one, but a backward bifurcation indicates that reducing the reproduction number below unity may not suffice for elimination. Sensitivity analysis identified the transmission rate among vaccinated individuals, breakthrough infections, and waning immunity as dominant drivers of transmission. Simulations demonstrated that while routine vaccination delays and reduces outbreak peaks, it does not interrupt transmission alone; annual campaigns outperform biennial strategies, preventing 40% more cases; and combined vaccination reduces the reproduction number below unity while preventing 65-80% of infections versus no vaccination. Critically, temporary disruptions in routine coverage significantly increase outbreak risk, and maintaining vaccine efficacy above 90% alongside hospitalization of at least 50% of infectious individuals is essential for containment. These results underscore that high-coverage routine vaccination must be integrated with periodic high-intensity campaigns and robust clinical care to close immunity gaps, mitigate waning protection, and accelerate measles elimination.</p>