Current scenario of COVID-19 vaccinations and immune response along with antibody titer in vaccinated inhabitants of different countries

Hussain, Asim; Rafeeq, Hamza; Memoona Asif, Hafiza; Shabbir, Sumaira; Bilal, Muhammad; Mulla, Sikandar I.; Franco, Marcelo; Iqbal, Hafiz M.N.

The COVID-19 pandemic challenges have been only partially addressed so far. The pathogenicity of SARS-CoV-2 is considered the combination of severe and high infectivity. Herd immunity is attained when a critical proportion of the population is immune, providing the virus with fewer chances to spread locally. To overcome the rising tide of the COVID-19 pandemic, efficacious and safe vaccines providing defensive and long-lasting immunity responses are urgently needed. Vaccines that induce virus-neutralizing antibodies with great affinity can optimally fight against infection. Worldwide, over 120 novel vaccine candidates, including live-attenuated, inactivated, viral-vectored nonreplicating and replicating, peptide- and protein-based, and nucleic acid-based approaches are in the process of preclinical and clinical trials (phase 1 to 4). In addition to comprehensive safety assessments and immune responses, precise clinical management is also important for trials of vaccines. The recent emergence of different variants of SARS-CoV-2 is becoming a new threat for the world and a challenge for scientists to introduce the most influential vaccine against COVID-19. The possibility of natural and vaccine-induced immunity in variants finds it necessary to establish next-generation vaccines, which generate general neutralization against existing and future variants. Here, we summarize the cellular and humoral responses of SARS-CoV-2, current progress in vaccination development, the antibody titer response of available phase 4 vaccinations in vaccinated populations of different countries worldwide, and the success and challenges ahead of vaccine development.