SARS-COV-2/COVID-19: scenario, epidemiology, adaptive mutations, and environmental factors.

The coronavirus pandemic of 2019 has already exerted an enormous impact. For over a year, the worldwide pandemic has ravaged the whole globe, with approximately 250 million verified human infection cases and a mortality rate surpassing 4 million. While the genetic makeup of the related pathogen (SARS-CoV-2) was identified, many unknown facets remain a mystery, comprising the virus's origin and evolutionary trend. There were many rumors that SARS-CoV-2 was human-borne and its evolution was predicted many years ago, but scientific investigation proved them wrong and concluded that bats might be the origin of SARS-CoV-2 and pangolins act as intermediary species to transmit the virus from bats to humans. Airborne droplets were found to be the leading cause of human-to-human transmission of this virus, but later studies showed that contaminated surfaces and other environmental factors are also involved in its transmission. The evolution of different SARS-CoV-2 variants worsens the condition and has become a challenge to overcome this pandemic. The emergence of COVID-19 is still a mystery, and scientists are unable to explain the exact origin of SARS-CoV-2. This review sheds light on the possible origin of SARS-CoV-2, its transmission, and the key factors that worsen the situation.

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. Herdimmunity 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.