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

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 1–4). 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.