Nucleic acid biomarkers of immune response and cell and tissue damage in children with COVID-19 and MIS-C

Differential host responses in coronavirus disease 2019 (COVID-19) and multisystem inflammatory syndrome in children (MIS-C) remain poorly characterized. Here we use next-generation sequencing to longitudinally analyze blood samples from pediatric patients with acute COVID-19 (n=70) or MIS-C (n=141) across three hospitals. Profiling of plasma cell-free nucleic acids uncovers distinct signatures of cell injury and death between COVID-19 and MIS-C, with increased multi-organ involvement in MIS-C encompassing diverse cell types including endothelial and neuronal cells, and an enrichment of pyroptosis related genes. Whole blood RNA profiling reveals upregulation of similar pro-inflammatory pathways in COVID-19 and MIS-C, but also MIS-C specific downregulation of T cell-associated pathways. Profiling of plasma cell-free RNA and whole blood RNA in paired samples yields different yet complementary signatures for each disease state. Our work provides a systems-level view of immune responses and tissue damage in COVID-19 and MIS-C and informs the future development of new disease biomarkers. Graphical Loy et al. use cell-free RNA, whole blood RNA, and cell-free DNA sequencing to characterize distinct host response and cellular injury profiles in pediatric patients with MIS-C and/or COVID-19. This study highlights the complementary information from cell-free and whole blood RNA analyses, with broad implications for future liquid biopsy applications.

Neutralizing Immunity Induced Against the Omicron BA.1 and BA.2 Variants in Vaccine Breakthrough Infections.

BACKGROUND: As of early 2022, the Omicron variants are the predominant circulating lineages globally. Understanding neutralizing antibody responses against Omicron BA.1 and BA.2 after vaccine breakthrough infections will provide insights into BA.2 infectivity and susceptibility to subsequent reinfection. METHODS: Live virus neutralization assays were used to study immunity against Delta and Omicron BA.1 and BA.2 variants in samples from 86 individuals, 24 unvaccinated (27.9%) and 62 vaccinated (72.1%), who were infected with Delta (n = 42, 48.8%) or BA.1 (n = 44, 51.2%). Among the 62 vaccinated individuals, 39 were unboosted (62.9%), whereas 23 were boosted (37.1%). RESULTS: In unvaccinated infections, neutralizing antibodies (nAbs) against the three variants were weak or undetectable, except against Delta for Delta-infected individuals. Both Delta and BA.1 breakthrough infections resulted in strong nAb responses against ancestral wild-type and Delta lineages, but moderate nAb responses against BA.1 and BA.2, with similar titers between unboosted and boosted individuals. Antibody titers against BA.2 were generally higher than those against BA.1 in breakthrough infections. CONCLUSIONS: These results underscore the decreased immunogenicity of BA.1 compared to BA.2, insufficient neutralizing immunity against BA.2 in unvaccinated individuals, and moderate to strong neutralizing immunity induced against BA.2 in Delta and BA.1 breakthrough infections.

COVID-19 Variant Detection with a High-Fidelity CRISPR-Cas12 Enzyme.

Laboratory tests for the accurate and rapid identification of SARS-CoV-2 variants can potentially guide the treatment of COVID-19 patients and inform infection control and public health surveillance efforts. Here, we present the development and validation of a rapid COVID-19 variant DETECTR assay incorporating loop-mediated isothermal amplification (LAMP) followed by CRISPR-Cas12 based identification of single nucleotide polymorphism (SNP) mutations in the SARS-CoV-2 spike (S) gene. This assay targets the L452R, E484K/Q/A, and N501Y mutations, at least one of which is found in nearly all major variants. In a comparison of three different Cas12 enzymes, only the newly identified enzyme CasDx1 was able to accurately identify all targeted SNP mutations. An analysis pipeline for CRISPR-based SNP identification from 261 clinical samples yielded a SNP concordance of 97.3% and agreement of 98.9% (258 of 261) for SARS-CoV-2 lineage classification, using SARS-CoV-2 whole-genome sequencing and/or real-time RT-PCR as test comparators. We also showed that detection of the single E484A mutation was necessary and sufficient to accurately identify Omicron from other major circulating variants in patient samples. These findings demonstrate the utility of CRISPR-based DETECTR as a faster and simpler diagnostic method compared with sequencing for SARS-CoV-2 variant identification in clinical and public health laboratories.

Limited cross-variant immunity from SARS-CoV-2 Omicron without vaccination.

SARS-CoV-2 Delta and Omicron are globally relevant variants of concern. Although individuals infected with Delta are at risk of developing severe lung disease, infection with Omicron often causes milder symptoms, especially in vaccinated individuals1,2. The question arises of whether widespread Omicron infections could lead to future cross-variant protection, accelerating the end of the pandemic. Here we show that without vaccination, infection with Omicron induces a limited humoral immune response in mice and humans. Sera from mice overexpressing the human ACE2 receptor and infected with Omicron neutralize only Omicron, but not other variants of concern, whereas broader cross-variant neutralization was observed after WA1 and Delta infections. Unlike WA1 and Delta, Omicron replicates to low levels in the lungs and brains of infected animals, leading to mild disease with reduced expression of pro-inflammatory cytokines and diminished activation of lung-resident T cells. Sera from individuals who were unvaccinated and infected with Omicron show the same limited neutralization of only Omicron itself. By contrast, Omicron breakthrough infections induce overall higher neutralization titres against all variants of concern. Our results demonstrate that Omicron infection enhances pre-existing immunity elicited by vaccines but, on its own, may not confer broad protection against non-Omicron variants in unvaccinated individuals.

Neutralizing immunity in vaccine breakthrough infections from the SARS-CoV-2 Omicron and Delta variants.

Virus-like particle (VLP) and live virus assays were used to investigate neutralizing immunity against Delta and Omicron SARS-CoV-2 variants in 259 samples from 128 vaccinated individuals. Following Delta breakthrough infection, titers against WT rose 57-fold and 3.1-fold compared with uninfected boosted and unboosted individuals, respectively, versus only a 5.8-fold increase and 3.1-fold decrease for Omicron breakthrough infection. Among immunocompetent, unboosted patients, Delta breakthrough infections induced 10.8-fold higher titers against WT compared with Omicron (p = 0.037). Decreased antibody responses in Omicron breakthrough infections relative to Delta were potentially related to a higher proportion of asymptomatic or mild breakthrough infections (55.0% versus 28.6%, respectively), which exhibited 12.3-fold lower titers against WT compared with moderate to severe infections (p = 0.020). Following either Delta or Omicron breakthrough infection, limited variant-specific cross-neutralizing immunity was observed. These results suggest that Omicron breakthrough infections are less immunogenic than Delta, thus providing reduced protection against reinfection or infection from future variants.

Predominance of antibody-resistant SARS-CoV-2 variants in vaccine breakthrough cases from the San Francisco Bay Area, California.

Associations between vaccine breakthrough cases and infection by different SARS coronavirus 2 (SARS-CoV-2) variants have remained largely unexplored. Here we analysed SARS-CoV-2 whole-genome sequences and viral loads from 1,373 persons with COVID-19 from the San Francisco Bay Area from 1 February to 30 June 2021, of which 125 (9.1%) were vaccine breakthrough infections. Vaccine breakthrough infections were more commonly associated with circulating antibody-resistant variants carrying ≥1 mutation associated with decreased antibody neutralization (L452R/Q, E484K/Q and/or F490S) than infections in unvaccinated individuals (78% versus 48%, P = 1.96 × 10-8). Differences in viral loads were non-significant between unvaccinated and fully vaccinated cases overall (P = 0.99) and according to lineage (P = 0.09-0.78). Symptomatic vaccine breakthrough infections had comparable viral loads (P = 0.64), whereas asymptomatic breakthrough infections had decreased viral loads (P = 0.023) compared with infections in unvaccinated individuals. In 5 cases with serial samples available for serologic analyses, vaccine breakthrough infections were found to be associated with low or undetectable neutralizing antibody levels attributable to an immunocompromised state or infection by an antibody-resistant lineage. Taken together, our results show that vaccine breakthrough infections are overrepresented by antibody-resistant SARS-CoV-2 variants, and that symptomatic breakthrough infections may be as efficient in spreading COVID-19 as unvaccinated infections, regardless of the infecting lineage.