Abstract
Influenza A viruses are dynamically epidemic and genetically diverse. Due to the antigenic drift and shift of the virus, seasonal vaccines are required to be reformulated annually to match with current circulating strains. However, the mismatch between vaccinal strains and circulating strains occurs frequently, resulting in the low efficacy of seasonal vaccines. Therefore, several “universal” vaccine candidates based on the structure and function of the hemagglutinin (HA) protein have been developed to meet the requirement of a broad protection against homo-/heterosubtypic challenges. Here, we review recent novel constructs and discuss several important findings regarding the broad protective efficacy of HA-based universal vaccines.
Highlights
According to the World Health Organization (WHO), influenza A viruses (IAVs) annually cause about 3 to 5 million cases of severe illness and approximately 290,000 to 650,000 respiratory deaths worldwide [1]
Based on the genetical differences of the HA amino acid sequences, IAVs are phylogenetically classified into two groups: group I and group II [4,5]
Among different HA subtypes, H1, H2, H5, H6, H8, H9, H11, H12, H13, H16, H17 and H18 belong to group I, whereas H3, H4, H7, H10, H14, H15 belong to group II
Summary
According to the World Health Organization (WHO), influenza A viruses (IAVs) annually cause about 3 to 5 million cases of severe illness and approximately 290,000 to 650,000 respiratory deaths worldwide [1]. The mixed infection of different IAV subtypes leads to the generation of re-assorted viruses. Several researchers have explored the reassortment of two different influenza subtypes in cells or animals [22,23,24] This phenomenon is referred to as “antigenic shift” [25]. Because of the absence of pre-existing immunity in the human immune system, the re-assorted IAVs (usually from avian and porcine origins) contribute to irregular pandemics [26,27], and caused at least the last three pandemics [28]. These pandemic strains are antigenically distinct from the circulating seasonal strains. We will discuss HA-based approaches, including our own, on designing universal influenza vaccines in recent years
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