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1.
Emerg Infect Dis ; 28(5): 998-1001, 2022 05.
Article in English | MEDLINE | ID: covidwho-1742173

ABSTRACT

To determine virus shedding duration, we examined clinical samples collected from the upper respiratory tracts of persons infected with severe acute respiratory syndrome coronavirus 2 Omicron variant in Japan during November 29-December 18, 2021. Vaccinees with mild or asymptomatic infection shed infectious virus 6-9 days after onset or diagnosis, even after symptom resolution.


Subject(s)
COVID-19 , Communicable Diseases , Asymptomatic Infections , Humans , SARS-CoV-2 , Virus Shedding
2.
Clin Infect Dis ; 2022 Jan 03.
Article in English | MEDLINE | ID: covidwho-1740823

ABSTRACT

In November 2021, the World Health Organization designated a new SARS-CoV-2 variant of concern, Omicron (PANGO lineage B.1.1.529). We report on first two cases of breakthrough COVID-19 caused by Omicron in Japan among international travelers returning from the country with undetected infection. The spread of infection by Omicron were considered.

3.
EuropePMC; 2021.
Preprint in English | EuropePMC | ID: ppcovidwho-305709

ABSTRACT

Since little is known about viral and host characteristics of breakthrough infections after COVID-19 vaccination, a nationwide investigation of breakthrough cases was initiated in Japan. 130 cases (90%+ received mRNA vaccines) were reported with respiratory specimens in 117 cases and sera in 68 cases. A subset of cases shed infectious virus regardless of symptom presence or viral lineages. Viral lineages for breakthrough infections matched both temporally and spatially with the circulating lineages in Japan with no novel mutations in spike receptor binding domain that may have escaped from vaccine-induced immunity were found. Anti-spike/neutralizing antibodies of breakthrough infections in the acute phase owing to vaccine-induced immunity were significantly higher than those from unvaccinated convalescent individuals but were comparable to vaccinated uninfected individuals, and followed by boosting in the convalescent phase. Symptomatic cases had low anti-spike/neutralizing antibodies in the acute phase with robust boosting in the convalescent phase, suggesting the presence of serological correlate for symptom development in COVID-19 vaccine breakthrough infections.

4.
Immunity ; 54(8): 1841-1852.e4, 2021 08 10.
Article in English | MEDLINE | ID: covidwho-1293863

ABSTRACT

Antibody titers against SARS-CoV-2 slowly wane over time. Here, we examined how time affects antibody potency. To assess the impact of antibody maturation on durable neutralizing activity against original SARS-CoV-2 and emerging variants of concern (VOCs), we analyzed receptor binding domain (RBD)-specific IgG antibodies in convalescent plasma taken 1-10 months after SARS-CoV-2 infection. Longitudinal evaluation of total RBD IgG and neutralizing antibody revealed declining total antibody titers but improved neutralization potency per antibody to original SARS-CoV-2, indicative of antibody response maturation. Neutralization assays with authentic viruses revealed that early antibodies capable of neutralizing original SARS-CoV-2 had limited reactivity toward B.1.351 (501Y.V2) and P.1 (501Y.V3) variants. Antibodies from late convalescents exhibited increased neutralization potency to VOCs, suggesting persistence of cross-neutralizing antibodies in plasma. Thus, maturation of the antibody response to SARS-CoV-2 potentiates cross-neutralizing ability to circulating variants, suggesting that declining antibody titers may not be indicative of declining protection.


Subject(s)
Antibodies, Neutralizing/immunology , Antibodies, Viral/immunology , COVID-19/immunology , COVID-19/virology , SARS-CoV-2/immunology , Antibodies, Monoclonal/immunology , Antibody Specificity , COVID-19/epidemiology , Humans , Immunoglobulin G , Neutralization Tests , SARS-CoV-2/genetics , Viral Load
5.
Proc Natl Acad Sci U S A ; 118(27)2021 07 06.
Article in English | MEDLINE | ID: covidwho-1276013

ABSTRACT

The spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) plays a key role in viral infectivity. It is also the major antigen stimulating the host's protective immune response, specifically, the production of neutralizing antibodies. Recently, a new variant of SARS-CoV-2 possessing multiple mutations in the S protein, designated P.1, emerged in Brazil. Here, we characterized a P.1 variant isolated in Japan by using Syrian hamsters, a well-established small animal model for the study of SARS-CoV-2 disease (COVID-19). In hamsters, the variant showed replicative abilities and pathogenicity similar to those of early and contemporary strains (i.e., SARS-CoV-2 bearing aspartic acid [D] or glycine [G] at position 614 of the S protein). Sera and/or plasma from convalescent patients and BNT162b2 messenger RNA vaccinees showed comparable neutralization titers across the P.1 variant, S-614D, and S-614G strains. In contrast, the S-614D and S-614G strains were less well recognized than the P.1 variant by serum from a P.1-infected patient. Prior infection with S-614D or S-614G strains efficiently prevented the replication of the P.1 variant in the lower respiratory tract of hamsters upon reinfection. In addition, passive transfer of neutralizing antibodies to hamsters infected with the P.1 variant or the S-614G strain led to reduced virus replication in the lower respiratory tract. However, the effect was less pronounced against the P.1 variant than the S-614G strain. These findings suggest that the P.1 variant may be somewhat antigenically different from the early and contemporary strains of SARS-CoV-2.


Subject(s)
COVID-19/virology , SARS-CoV-2/physiology , SARS-CoV-2/pathogenicity , Virus Replication , Animals , Antibodies, Neutralizing , COVID-19/diagnostic imaging , COVID-19/pathology , Cricetinae , Humans , Immunogenicity, Vaccine , Lung/pathology , Mesocricetus , Mice , Spike Glycoprotein, Coronavirus/genetics , X-Ray Microtomography
6.
Emerg Infect Dis ; 27(4)2021 04.
Article in English | MEDLINE | ID: covidwho-1145545

ABSTRACT

Multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with higher transmission potential have been emerging globally, including SARS-CoV-2 variants from the United Kingdom and South Africa. We report 4 travelers from Brazil to Japan in January 2021 infected with a novel SARS-CoV-2 variant with an additional set of mutations.


Subject(s)
COVID-19/drug therapy , Communicable Diseases, Imported , SARS-CoV-2 , Adult , Basic Reproduction Number , Brazil/epidemiology , COVID-19/epidemiology , COVID-19/therapy , COVID-19/transmission , COVID-19/virology , Communicable Diseases, Imported/epidemiology , Communicable Diseases, Imported/physiopathology , Communicable Diseases, Imported/therapy , Communicable Diseases, Imported/virology , Hospitalization , Humans , Japan/epidemiology , Male , Mutation , Quarantine/methods , SARS-CoV-2/genetics , SARS-CoV-2/isolation & purification , Symptom Assessment/methods , Travel-Related Illness , Treatment Outcome
7.
BMJ Open Respir Res ; 8(1)2021 02.
Article in English | MEDLINE | ID: covidwho-1102195

ABSTRACT

BACKGROUND: An outbreak of novel coronavirus (SARS-CoV-2)-associated respiratory infectious diseases (COVID-19) emerged in 2019 and has spread rapidly in humans around the world. The demonstration of in vitro infectiousness of respiratory specimens is an informative surrogate for SARS-CoV-2 transmission from patients with COVID-19; accordingly, viral isolation assays in cell culture are an important aspect of laboratory diagnostics for COVID-19. METHODS: We developed a simple and rapid protocol for isolating SARS-CoV-2 from respiratory specimens using VeroE6/TMPRSS2 cells, a cell line that is highly susceptible to the virus. We also investigated a correlation between isolation of SARS-CoV-2 and viral load detected by real-time RT-PCR (rRT-PCR) using N2 primer/probe set that has been developed for testing of COVID-19 in Japan. RESULTS: The SARS-CoV-2 isolation protocol did not require blind passage of inoculated cells and yielded the results of viral isolation within 7 days after inoculation. Specimens with cycle threshold (Ct) values of <20.2, determined by rRT-PCR, were predicted to be isolation-positive. On the other hand, 6.9% of specimens with Ct values >35 were virus isolation-positive, indicating that low viral loads (high Ct values) in upper respiratory specimens do not always indicate no risk of containing transmissible virus. CONCLUSION: In combination with rRT-PCR, the SARS-CoV-2 isolation protocol provides a means for assessing the potential risk of transmissible virus in upper respiratory specimens.


Subject(s)
COVID-19/transmission , SARS-CoV-2/pathogenicity , Animals , COVID-19 Nucleic Acid Testing , Cell Line , Chlorocebus aethiops , Cytopathogenic Effect, Viral , Humans , Nasal Cavity/virology , Nasopharynx/virology , SARS-CoV-2/isolation & purification , Saliva/virology , Serine Endopeptidases/genetics , Specimen Handling , Vero Cells
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