Kolaib, Tamer M., and Rehab M. Sabry. 2021. “Heterologous COVID-19 Vaccinations of Covishield/Astrazenica and Pfizer/Biontech: A Case Report”. International Journal of Research in Medical Sciences 9 (11):3454-56. https://doi.org/10.18203/2320-6012.ijrms20214428.