Modern vaccine strategies for emerging zoonotic viruses

ABSTRACT

Introduction

The significant increase in the emergence of notable zoonotic viruses in the previous decades has become a serious concern to global public health. Ninety-nine percent of infectious diseases have originated from zoonotic viruses with immense potential for dissemination, infecting the susceptible population completely lacking herd immunity.

Areas Covered

Zoonotic viruses appear in the last two decades as a major health threat either newly evolved or previously present with elevated prevalence in the last few years are selected to explain their current prophylactic measures. In this review, modern generation vaccines including viral vector vaccines, mRNA vaccines, DNA vaccines, synthetic vaccines, virus-like particles, and plant-based vaccines are discussed with their benefits and challenges. Moreover, the traditional vaccines and their efficacy are also compared with the latest vaccines.

Expert Opinion

The emergence and reemergence of viruses that constantly mutate themselves have greatly increased the chance of transmission and immune escape mechanisms in humans. Therefore, the only possible solution to prevent viral infection is the use of vaccines with improved safety profile and efficacy, which becomes the basis of modern generation vaccines.

GRAPHICAL ABSTRACT

KEYWORDS:

• Immune response
• zoonotic virus
• herd immunity
• pathogen
• vaccine
• viral vectors

Article highlights

• Zoonotic viruses are emerging public health threats to humans with most infectious diseases constantly emerging from viral origin. The respiratory route of transmission is mainly responsible for the immense disseminating potential of zoonotic viruses.

• Multiple therapeutic alternatives are available in the world, but vaccines are the only effective strategy to protect mankind from viral infections.

• The earlier generation vaccines have been effective in past times when limited treatment options were available, but they stimulate low-level immune response with poor safety profiles. Moreover, attenuated and killed vaccines are difficult to develop and are mostly ineffective to provoke an optimum immune response against zoonotic viruses.

• The modern generations have overcome the issues of safety profiles and the ability to elicit an effective immune response against viruses by utilizing modern molecular biology techniques and bioinformatics tools.

• Viral vectors contain the core of viruses; however, they are non-pathogenic but highly immunogenic entities with replication-competent, replication-defective, single-cycle viral vectors and multi-segment viral vector approaches to synthesize the vaccine.

• mRNA vaccine contains self-amplifying mRNA or non-amplifying mRNA with fewer modifications in a lipid shell. The non-amplifying mRNA utilizes the host cell machinery for antigen expression, while self-amplifying mRNA brings translation machinery along with antigenic mRNA transcript. These vaccines stimulate the effective and extended immune response.

• The hollow, non-infectious structure of the viral coat is utilized to evoke a vigorous humoral and cell-mediated immune response in the host. The coat contains all the antigenic proteins present in the virulent virus.

• DNA vaccines are based on a plasmid containing the sequence for antigenic proteins, which are expressed intracellularly to produce an immune response in the host in humoral and cell-mediated branches of immunity.

• Various antigenic peptides are combined to produce a subunit vaccine in which only antigenic determinants of viral surface proteins are expressed to trigger an immune response.

The recombinant proteins are expressed in the plant in stable or transient form to express either VLPs or antigenic proteins with the production of fruit. These antigenic proteins are an edible and cost-effective method of production at a high scale.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or material discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or mending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Author contributions

A Ahmed wrote the Abstract, Introduction, Earlier generation vaccines, viral vectors, mRNA, VLP, DNA vaccines, and expert opinion. Moreover, he also drew the first 3 tables. M Safdar wrote the plant-based vaccines and drew all figures. He also set the references of the article. S Yousaf wrote the synthetic peptides. S Sardar, F Farooq, and A Raza helped in searching for related scientific material.

Additional information

Funding

This paper was funded by the National Research Program for Universities, Higher Education Commission of Pakistan.