Abstract
PURPOSE OF REVIEW: The emergence of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has affected lives of billions of individuals, globally. There is an urgent need to develop interventions including vaccines to control the ongoing pandemic. RECENT FINDINGS: Development of tools for fast-tracked testing including small and large animal models for vaccine efficacy analysis, assays for immunogenicity assessment, critical reagents, international biological standards, and data sharing allowed accelerated development of vaccines. More than 300 vaccines are under development and 9 of them are approved for emergency use in various countries, with impressive efficacy ranging from 50 to 95%. Recently, several new SARS-CoV-2 variants have emerged and are circulating globally, and preliminary findings imply that some of them may escape immune responses against previous variants and diminish efficacy of current vaccines. Most of these variants acquired new mutations in their surface protein (Spike) which is the antigen in most of the approved/under development vaccines. SUMMARY: In this review, we summarize novel and traditional approaches for COVID-19 vaccine development including inactivated, attenuated, nucleic acid, vector and protein based. Critical assessment of humoral and cell-mediated immune responses induced by vaccines has shown comparative immunogenicity profiles of various vaccines in clinical phases. Recent reports confirmed that some currently available vaccines provide partial to complete protection against emerging SARS-CoV-2 variants. If more mutated variants emerge, current vaccines might need to be updated accordingly either by developing vaccines matching the circulating strain or designing multivalent vaccines to extend the breadth.