Hajra Farooq, Omar Rasheed Chughtai, Hijab Batool, Waheed uz Zaman Tariq, and Akhtar Sohail Chughtai, “Comparison of Covid-19 IgG Anti-Spike Antibody Titer after Vaccination with Sputnik V in Seropositive and Naïve Vaccinees ”, Proceedings S.Z.M.C, vol. 35, no. 4, pp. 1–5, Nov. 2021.