SARS-CoV-2 Vaccination and the Bridge between First and Fourth Dose: Where Are We?

Cristina Stasi,Fabio Voller,Barbara Meoni,Caterina Silvestri

doi:10.3390/vaccines10030444

Abstract

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has induced the explosion of vaccine research. Currently, according to the data of the World Health Organization, there are several vaccines in clinical (145) and preclinical (195) stages, while at least 10 are already in clinical phase 4 (post-marketing). Vaccines have proven to be safe, effective, and able to reduce the spread of SARS-CoV-2 infection and its variants, as well as the clinical consequences of the development of coronavirus disease-19 (COVID-19). In the two-dose primary vaccination, different time intervals between the two doses have been used. Recently, special attention has been paid to assessing the immunogenicity following booster administration. The third dose of the vaccine against COVID-19 may be administered at least 8 weeks after the second dose. In Israel, a fourth dose has already been approved in immunocompromised groups. The main objective of this review is to describe the principal results of studies on the effectiveness of first-to-fourth dose vaccination to reduce reinfection by variants and the incidence of severe disease/death caused by COVID-19. Vaccines have shown a high level of protection from symptomatic infection and reinfection by variants after a third dose. Accelerating mass third-dose vaccination could potentially induce immunogenicity against variants.

Highlights

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has induced the explosion of vaccine research
Lower risk of infection) for the subsequent 7 months. These findings suggest that a single-dose vaccination strategy could be adopted for individuals with prior COVID-19 or they could be placed further down the vaccination priority list on the basis of the antibody titer
Despite the small sample size and possible selection bias, this study demonstrated that, against SARS-CoV-2 variants, including B.1, B.1.1.7, and N501Y, antibody neutralizing activity induced by both vaccine and infection is present

Summary

Introduction

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has induced the explosion of vaccine research. In addition to traditional inactivated or live-attenuated vaccines, the context of COVID-19’s emergence has resulted in the need to find a safe vector for antigen and gene delivery and to design nucleic acid-based vaccines (vaccines mRNA and DNA) and subunit vaccines. Many of these new vaccines have been designed by encapsulating nucleic acids or peptides/proteins within polymer and lipid nanoparticles [1]. According to the World Health Organization data, there are currently 145 vaccines in clinical development and 195 in preclinical development, while there are RNA-based (N = 3), viral vector (N = 3), inactivated virus (N = 3), and protein subunit (N = 1) [3]

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