“Estimating the Amount of Defective Vaccines and their Impact on the Environment Using A System of Simultaneous Equation” (2024) Journal of Al-Rafidain University College For Sciences ( Print ISSN: 1681-6870 ,Online ISSN: 2790-2293 ), 54(1), pp. 292–302. doi:10.55562/jrucs.v54i1.599.