Waned vaccine-induced immunity and emerging severe acute respiratory syndrome coronavirus 2 variants with potential for immune escape pose a major threat to the coronavirus disease (COVID-19) pandemic. Here, we showed that humoral immunity components, including anti-S + N, anti-RBD IgG, and neutralizing antibodies (NAbs), gradually waned and decreased the neutralizing capacity against emerging Omicron variants at 3 and 6 months after two inactivated COVID-19 vaccinations. We evaluated two boosting strategies with either a third dose of inactivated vaccine (homologous, I-I-I) or a recombinant subunit vaccine (heterologous, I-I-S). Both strategies induced the production of high levels of NAbs with a broad neutralizing capacity and longer retention. Interestingly, I-I-S induced 3.5-fold to 6.8-fold higher NAb titres than I-I-I, with a broader neutralizing capacity against six variants of concern, including Omicron. Further immunological analysis revealed that the two immunization strategies differ considerably, not only in the magnitude of total NAbs produced, but also in the composite pattern of NAbs and the population of virus-specific CD4+ T cells produced. Additionally, in some cases, heterologous boosted immunity induced the production of more effective epitopes than natural infection. The level of I-I-S-induced NAbs decreased to 48% and 18% at 1 and 3 months after booster vaccination, respectively. Overall, our data provide important evidence for vaccination strategies based on available vaccines and may help guide future global vaccination plans.

Influenza A virus (IAV) is an eight-segment negative-sense RNA virus and is subjected to gene recombination between strains to form novel strains, which may lead to influenza pandemics. Seasonal influenza occurs annually and causes great losses in public healthcare. In this study, we examined the role of interferon-induced protein with tetratricopeptide repeats 1 and 2 (IFIT1 and IFIT2) in influenza virus infection. Knockdown of IFIT1 or IFIT2 using a lentiviral shRNA increased viral nucleoprotein (NP) and nonstructural protein 1 (NS1) protein levels, as well as progeny virus production in A/Puerto Rico/8/34 H1N1 (PR/8)-infected lung epithelial A549 cells. Overexpression of IFIT1 or IFIT2 reduced viral NP and NS1 RNA and protein levels in PR/8-infected HEK293 cells. Overexpression of IFIT1 or IFIT2 also inhibited influenza virus infection of various H1N1 strains, including PR/8, A/WSN/1933, A/California/07/2009 and A/Oklahoma/3052/2009, as determined by a viral reporter luciferase assay. Furthermore, knockdown of IFIT1 or IFIT2 increased while overexpression of IFIT1 or IFIT2 decreased viral RNA, complementary RNA, and mRNA levels of NP and NS1, as well as viral polymerase activities. Taken together, our results support that both IFIT1 and -2 have anti-influenza virus activities by inhibiting viral RNA synthesis.

Traditional polysaccharide vaccines are constrained by streptococcus pneumoniae diversity. We propose a protein-based pneumococcal vaccine (PBPV) — formulated with conserved surface proteins P3296, P5668, PRx1, and pneumolysin (Ply) — that could potentially offer superior immune breadth independent of capsular polysaccharide serotypes. Here, we evaluated the multifunctional antibody responses induced by PBPV, including immunogenicity, Ply neutralization, opsonophagocytic activity (OPA), and such nonopsonic functions as NK cell activation (ADNKA), antibody-dependent cellular phagocytosis, and neutrophil phagocytosis (ADNP) in a cohort of 50- to 69-year-olds. While PBPV showed shorter-lasting immune responses, including reduced Ply-neutralizing capacity, it provided broader cross-serotype protection than 23-valent pneumococcal polysaccharide vaccine. Correlation analysis identified distinct PspA-specific IgG subclass roles: P3296-IgG1 correlated with OPA, and IgG3 correlated with ADNKA/ADNP; P5668-IgG2 correlated with ADNKA/ADNP, and IgG3 correlated with OPA; and PRx1-IgG2 correlated with OPA, and IgG3 correlated with ADNKA. Critically, while no efficacy data have yet confirmed the protective effect of PBPV, its targeting of conserved proteins rather than capsular polysaccharides enables simplified manufacturing and expanded coverage, positioning it as a promising alternative to traditional multipolysaccharide vaccines.