Attenuation mechanism leads to unequally distributed synthesis of viral mRNAs and proteins. The partial transcription termination mechanism (or attenuation) is common in (-)ssRNA viruses. This mechanism is important to satisfy the different needs of each viral protein during its infection cycle. Five attenuation factors for each intergenic region of the VSV genome (Table 1 and Equation 8 ) were obtained from the literature [18, 19, 26, 27] and incorporated into our model.