Abstract
Influenza viruses pose a significant threat to human health. They are responsible for a large number of deaths annually and have a serious impact on the global economy. There are numerous influenza virus subtypes, antigenic variations occur continuously, and epidemic trends are difficult to predict—all of which lead to poor outcomes of routine vaccination against targeted strain subtypes. Therefore, the development of universal influenza vaccines still constitutes the ideal strategy for controlling influenza. This article reviews the progress in development of universal vaccines directed against the conserved regions of hemagglutinin (HA), neuraminidase (NA), and other structural proteins of influenza viruses using new technologies and strategies with the goals of enhancing our understanding of universal influenza vaccines and providing a reference for research into the exploitation of natural immunity against influenza viruses.
Highlights
Influenza viruses comprise enveloped RNA viruses with a genome composed of eight single-stranded negative-sense RNA fragments encoding polymerase subunits PA, PB1, and PB2, envelope proteins hemagglutinin (HA) and neuraminidase (NA), nucleoproteins (NP) binding to genomic RNA, matrix protein M1 and ion channel protein M2, nonstructural protein NS1, nuclear export protein NEP, and the more recently discovered PB1-F2, PB1 N40, PA-X, and M42 proteins [1,2,3,4,5].Annual seasonal outbreaks of influenza occur in winter and spring, which can seriously threaten the life of individuals with increased susceptibility to influenza such as the elderly, children, and those with low immunity
According to the statistics of the U.S Centers for Disease Control and Prevention (CDC), 39–56 million people were infected by influenza viruses from October 2019–April 2020, among whom
Organization (WHO), 3–5 million cases of severe respiratory disease induced by influenza virus infection occur every year
Summary
Influenza viruses comprise enveloped RNA viruses with a genome composed of eight single-stranded negative-sense RNA fragments encoding polymerase subunits PA, PB1, and PB2, envelope proteins hemagglutinin (HA) and neuraminidase (NA), nucleoproteins (NP) binding to genomic RNA, matrix protein M1 and ion channel protein M2, nonstructural protein NS1, nuclear export protein NEP, and the more recently discovered PB1-F2, PB1 N40, PA-X, and M42 proteins [1,2,3,4,5]. These vaccines offer weak inter-subtype cross-protection and exhibit high incidence of fever upon use in children. These vaccines have few side effects and high immunogenicity albeit weak inter-subtype cross-protection [10,11]. These cold-adapted strains can replicate effectively at 25–33 ◦ C their replication is limited at 37 ◦ C This type of vaccine can be administered via nasal drops, with the limited replication of viruses in the upper respiratory tract able to stimulate the body to produce high-levels of sIgA and cellular immune response, thereby generating strong cross-protection [12,13,14,15]. The target virus proteins and immune effects of universal vaccines are reviewed in order to analyze the advantages and disadvantages of different universal vaccine strategies and provide a theoretical basis for developing safe, effective, and quality-controllable universal influenza vaccines
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