Five doses of the mRNA vaccination potentially suppress ancestral-strain stimulated SARS-CoV2-specific cellular immunity: a cohort study from the Fukushima vaccination community survey, Japan

More antibodies are not always better: Fc effector functions play a critical role in SARS-CoV-2 infection and protection

Traditional vaccinology has primarily focused on neutralizing antibody titers as the main correlate of vaccine efficacy, often overlooking the multifaceted roles of antibody Fc effector functions in orchestrating protective immune responses. Fc-mediated immune responses play a pivotal role in immune modulation and pathogen clearance. Emerging evidence from natural infections and vaccine studies highlights the critical contribution of Fc effector functions in determining the quality and durability of immunity. This work explores the limitations of current vaccine evaluation paradigms that prioritize neutralization over Fc effector mechanisms. It also describes findings from a study showing an unexpected role for SARS-CoV-2 anti-spike antibodies: both convalescent plasma and patient-derived monoclonal antibodies (mAbs) lead to maximum phagocytic capacity by monocytes at low concentrations, whereas at higher concentrations the phagocytic capacity was reduced. Given that the severity of COVID-19 disease and antibody titers are strongly positively correlated, this work challenges the paradigm that high antibodies offer better protection against severe disease. It is proposed that humoral and cellular responses elicited by vaccination should never be higher than those produced by natural infection. By integrating antibody Fc effector functions into vaccine development, a paradigm shift is proposed that emphasizes synergic antibody responses. Such an approach could transform vaccine efficacy assessment, enhance protection against dangerous pathogens, and drive innovation in vaccine design.

Antibody Response After a Fifth Dose (Third Booster) of BNT162b2 mRNA COVID-19 Vaccine in Healthcare Workers

Although a fourth dose of SARS-CoV-2 vaccine was shown to be effective, the immunogenicity of a fifth dose in immunocompetent individuals had not been well described. This was a prospective observational cohort study of previously vaccinated healthcare workers at a single tertiary hospital in Israel. Individuals were administered up to three booster doses of the BNT162b2 mRNA vaccine (i.e., up to five overall doses), during the period between July 2021 and January 2023. Immunogenicity was assessed using the SARS-CoV-2 IgG (sCOVG) semi-quantitative assay, performed at several time points. The cohort consisted of 162 individuals (median age 69 years, 62% female). Of these, 104 (64%) received four doses and 58 (36%) received five doses. Anti-SARS-CoV-2 antibody levels increased in all cases, regardless of the baseline levels. The fold-change increase in the mean sCOVG index was 29.2 (SD 2.6) after the third vaccine, 3.8 (SD 2.4) after the fourth vaccine, and 3.6 (SD 3.0) after the fifth vaccine. A waning effect over time was seen in 78% and 43% of participants for the third and fourth doses, respectively. Adverse events following the fifth dose were limited and mild. Similar to previous booster vaccines, a fifth dose of BNT162b2 is immunogenic and safe in healthy individuals, although the clinical implications remain unclear.

Similar humoral responses but distinct CD4+ T cell transcriptomic profiles in older adults elicited by MF59 adjuvanted and high dose influenza vaccines

Older age (≥ 65 years) is associated with impaired responses to influenza vaccination, leading to the preferential recommendation of MF59-adjuvanted (MF59Flu) or high-dose (HDFlu) influenza vaccines for this age group in the United States. Herein, we characterized transcriptomic profiles of CD4+ T cells isolated from 234 recipients (≥ 65 years) of either MF59Flu or HDFlu vaccine, prior to vaccination and 28 days thereafter. We identified 412 and 645 differentially expressed genes (DEGs) in CD4+ T cells of older adults after receiving MF59Flu and HDFlu, respectively. DEGs in CD4+ T cells of MF59Flu recipients were enriched in 14 KEGG pathways, all of which were downregulated. DEGs in CD4+ T cells of HDFlu recipients were enriched in 11 upregulated pathways and 20 downregulated pathways. CD4+ T cells in both vaccine groups shared 50 upregulated genes and 75 downregulated genes, all of which were enriched in 7 KEGG pathways. The remaining 287 and 520 DEGs were specifically associated with MF59Flu and HDFlu, respectively. Unexpectedly, none of these DEGs was significantly correlated with influenza A/H3N2-specific HAI titers, suggesting these DEGs at the individual level may have a limited role in protection against influenza. Our findings emphasize the need for further investigation into other factors influencing immunity against influenza in older adults.

Heterologous booster vaccination enhances antibody responses to SARS-CoV-2 by improving Tfh function and increasing B-cell clonotype SHM frequency

Heterologous prime-boost has broken the protective immune response bottleneck of the COVID-19 vaccines. however, the underlying mechanisms have not been fully elucidated. Here, we investigated antibody responses and explored the response of germinal center (GC) to priming with inactivated vaccines and boosting with heterologous adenoviral-vectored vaccines or homologous inactivated vaccines in mice. Antibody responses were dramatically enhanced by both boosting regimens. Heterologous immunization induced more robust GC activation, characterized by increased Tfh cell populations and enhanced helper function. Additionally, increased B-cell activation and antibody production were observed in a heterologous regimen. Libra-seq was used to compare the differences of S1-, S2- and NTD-specific B cells between homologous and heterologous vaccination, respectively. S2-specific CD19+ B cells presented increased somatic hypermutations (SHMs), which were mainly enriched in plasma cells. Moreover, a heterologous booster dose promoted the clonal expansion of B cells specific to S2 and NTD regions. In conclusion, the functional role of Tfh and B cells following SARS-CoV-2 heterologous vaccination may be important for modulating antibody responses. These findings provide new insights for the development of SARS-CoV-2 vaccines that induce more robust antibody response.

Diminished neutralizing activity against the XBB1.5 strain in 55.9% of individuals post 6 months COVID-19 mRNA booster vaccination: insights from a pseudovirus assay on 1,353 participants in the Fukushima vaccination community survey, Japan

This study investigates the neutralizing activity against the XBB1.5 variant and the ancestral strain in a population post-bivalent vaccination using a pseudo virus assay validated with authentic virus assay. While bivalent booster vaccination and past infections enhanced neutralization against the XBB 1.5 strain, individuals with comorbidities showed reduced responses. The study suggests the need for continuous vaccine updates to address emerging SARS-CoV-2 variants and highlights the importance of monitoring real-world immune responses.

Humoral response against spike protein enhanced by fifth and sixth COVID-19 mRNA vaccine in the uninfected and infected subjects

Antibody obtained by the coronavirus disease-19 (COVID-19) mRNA vaccine declines over time, and additional vaccinations are offered. It is not clear how repeated vaccination affects humoral immunity in uninfected individuals. We analyzed immunoglobulin G for spike protein (S-IgG) titers in COVID-19 uninfected and infected individuals vaccinated up to six times. The geometric mean S-IgG titers were 575.9 AU/mL and 369.0 AU/mL in those who received 6 and 5 doses less than 180 days after the last vaccination in uninfected subjects. In the 180-360 days after the last vaccination, the geometric mean S-IgG titers were 237.9 AU/mL and 128.6 AU/mL in the uninfected subjects who underwent five-dose and four-dose groups, respectively. Multivariate analysis showed that S-IgG titer increased 1.261-fold with each additional dose of mRNA vaccine. The S-IgG titers were 2.039-fold higher in the COVID-infected subjects compared to uninfected subjects. The positivity rate of nucleocapsid antibodies, suggesting a history of COVID-19, decreased 82% and 30% of COVID-infected cases after 180 and 360 days of infection, respectively. This result suggested that repeated vaccination with the COVID-19 mRNA vaccine may increase antibody titer in uninfected subjects.