N'Debi, M. | Search bioRxiv

bioRxiv2026

Quantifying the mechanisms of vaccine-induced serotype replacement in Streptococcus pneumoniae using genome-informed modelling

Streptococcus pneumoniae is a colonizer of the childs nasopharynx and a leading cause of invasive pneumococcal disease (IPD). Despite widespread use of pneumococcal conjugate vaccines, recent rebounds in IPD incidence have coincided with serotype replacement. Whether this phenomenon is driven by the replacement of serotypes within lineages or the replacement of the lineages themselves is unclear. Here, we quantified the relative contribution of these two mechanisms to serotype replacement in carriage and their consequences for IPD. We combined nationwide longitudinal surveillance of carriage and IPD in children from 2002 to 2023 with whole-genome sequencing. Observed lineage-specific carriage rates across PCV-related periods were fitted with polynomial logistic regression and compared with two counterfactual scenarios, each isolating one mechanism with: (i) fixed serotype composition within varying lineages and (ii) serotype shifts within fixed lineage carriage rates over time. Carriage dynamics were consistent with an 82% contribution of serotype shifts within persistent lineages. Estimates of serotype-specific IPD incidence derived from this predominant scenario correlated with observed IPD trends. These findings quantify the dominant role of serotype replacement within persistent lineages, disentangling the vaccine-driven adaptive history of S. pneumoniae.

microbiology↗

bioRxiv2023

High fusion and cytopathy of SARS-CoV-2 variant B.1.640.1

SARS-CoV-2 variants with undetermined properties have emerged intermittently throughout the COVID-19 pandemic. Some variants possess unique phenotypes and mutations which allow further characterization of viral evolution and spike functions. Around 1100 cases of the B.1.640.1 variant were reported in Africa and Europe between 2021 and 2022, before the expansion of Omicron. Here, we analyzed the biological properties of a B.1.640.1 isolate and its spike. Compared to the ancestral spike, B.1.640.1 carried 14 amino acid substitutions and deletions. B.1.640.1 escaped binding by some anti-NTD and -RBD monoclonal antibodies, and neutralization by sera from convalescent and vaccinated individuals. In cell lines, infection generated large syncytia and a high cytopathic effect. In primary airway cells, B.1.640.1 replicated less than Omicron BA.1 and triggered more syncytia and cell death than other variants. The B.1.640.1 spike was highly fusogenic when expressed alone. This was mediated by two poorly characterized and infrequent mutations located in the spike S2 domain, T859N and D936H. Altogether, our results highlight the cytopathy of a hyper-fusogenic SARS-CoV-2 variant, supplanted upon the emergence of Omicron BA.1. ImportanceOur results highlight the plasticity of SARS-CoV-2 spike to generate highly fusogenic and cytopathic strains with the causative mutations being uncharacterized in previous variants. We describe mechanisms regulating the formation of syncytia and the subsequent consequences in cell lines and a primary culture model, which are poorly understood.

microbiology↗