Najeeb, Nida, Khaleel Ahmad, and Sahib Yar. “A Hilfer Fractional Vaccination Epidemic Model: Stability Analysis and a Physics-Informed Neural Network Validated on COVID-19 Data”. International Scientific Spectrum (September 13, 2026): 1–32. Accessed October 13, 2026. https://iscis-journal.org/index.php/iscis/article/view/21.