Differences among epitopes recognized by neutralizing antibodies induced by SARS-CoV-2 infection or COVID-19 vaccination.

SARS-CoV-2 has gradually acquired amino acid substitutions in its S protein that reduce the potency of neutralizing antibodies, leading to decreased vaccine efficacy. Here, we attempted to obtain mutant viruses by passaging SARS-CoV-2 in the presence of plasma samples from convalescent patients or vaccinees to determine which amino acid substitutions affect the antigenicity of SARS-CoV-2. Several amino acid substitutions in the S2 region, as well as the N-terminal domain (NTD) and receptor-binding domain (RBD), affected the neutralization potency of plasma samples collected from vaccinees, indicating that amino acid substitutions in the S2 region as well as those in the NTD and RBD affect neutralization by vaccine-induced antibodies. Furthermore, the neutralizing potency of vaccinee plasma samples against mutant viruses we obtained or circulating viruses differed among individuals. These findings suggest that genetic backgrounds of vaccinees influence the recognition of neutralizing epitopes.

Seroprevalence of SARS-CoV-2 antibodies in dogs and cats during the early and mid-pandemic periods in Japan.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has continued to circulate in humans since its emergence in 2019. While infection in humans continues, numerous spillover events to at least 32 animal species, including companion and zoo animals, have been reported. Since dogs and cats are highly susceptible to SARS-CoV-2 and have direct contact with their owners and other household members, it is important to know the prevalence of SARS-CoV-2 in dogs and cats. Here, we established an ELISA to detect serum antibodies against the receptor-binding domain and the ectodomain of the SARS-CoV-2 spike and nucleocapsid proteins. Using this ELISA, we assessed seroprevalence in 488 dog serum samples and 355 cat serum samples that were collected during the early pandemic period (between May and June of 2020) and 312 dog serum samples and 251 cat serum samples that were collected during the mid-pandemic period (between October 2021 and January 2022). We found that two dog serum samples (0.41%) collected in 2020, one cat serum sample (0.28%) collected in 2020, and four cat serum samples (1.6%) collected in 2021 were positive for antibodies against SARS-CoV-2. No dog serum samples collected in 2021 were positive for these antibodies. We conclude that the seroprevalence of SARS-CoV-2 antibodies in dogs and cats in Japan is low, suggesting that these animals are not a major SARS-CoV-2 reservoir.

Age-Stratified Seroprevalence of SARS-CoV-2 Antibodies before and during the Vaccination Era, Japan, February 2020-March 2022.

Japan has reported a relatively small number of COVID-19 cases. Because not all infected persons receive diagnostic tests for COVID-19, the reported number must be lower than the actual number of infections. We assessed SARS-CoV-2 seroprevalence by analyzing >60,000 samples collected in Japan (Tokyo Metropolitan Area and Hokkaido Prefecture) during February 2020-March 2022. The results showed that ≈3.8% of the population had become seropositive by January 2021. The seroprevalence increased with the administration of vaccinations; however, among the elderly, seroprevalence was not as high as the vaccination rate. Among children, who were not eligible for vaccination, infection was spread during the epidemic waves caused by the SARS-CoV-2 Delta and Omicron variants. Nevertheless, seroprevalence for unvaccinated children <5 years of age was as low as 10% as of March 2022. Our study underscores the low incidence of SARS-CoV-2 infection in Japan and the effects of vaccination on immunity at the population level.

Characterization and antiviral susceptibility of SARS-CoV-2 Omicron BA.2.

The recent emergence of SARS-CoV-2 Omicron (B.1.1.529 lineage) variants possessing numerous mutations has raised concerns of decreased effectiveness of current vaccines, therapeutic monoclonal antibodies and antiviral drugs for COVID-19 against these variants1,2. The original Omicron lineage, BA.1, prevailed in many countries, but more recently, BA.2 has become dominant in at least 68 countries3. Here we evaluated the replicative ability and pathogenicity of authentic infectious BA.2 isolates in immunocompetent and human ACE2-expressing mice and hamsters. In contrast to recent data with chimeric, recombinant SARS-CoV-2 strains expressing the spike proteins of BA.1 and BA.2 on an ancestral WK-521 backbone4, we observed similar infectivity and pathogenicity in mice and hamsters for BA.2 and BA.1, and less pathogenicity compared with early SARS-CoV-2 strains. We also observed a marked and significant reduction in the neutralizing activity of plasma from individuals who had recovered from COVID-19 and vaccine recipients against BA.2 compared to ancestral and Delta variant strains. In addition, we found that some therapeutic monoclonal antibodies (REGN10987 plus REGN10933, COV2-2196 plus COV2-2130, and S309) and antiviral drugs (molnupiravir, nirmatrelvir and S-217622) can restrict viral infection in the respiratory organs of BA.2-infected hamsters. These findings suggest that the replication and pathogenicity of BA.2 is similar to that of BA.1 in rodents and that several therapeutic monoclonal antibodies and antiviral compounds are effective against Omicron BA.2 variants.

Characterization of H9N2 Avian Influenza Viruses Isolated from Poultry Products in a Mouse Model.

Low pathogenic H9N2 avian influenza viruses have spread in wild birds and poultry worldwide. Recently, the number of human cases of H9N2 virus infection has increased in China and other countries, heightening pandemic concerns. In Japan, H9N2 viruses are not yet enzootic; however, avian influenza viruses, including H5N1, H7N9, H5N6, and H9N2, have been repeatedly detected in raw poultry meat carried by international flight passengers from Asian countries to Japan. Although H9N2 virus-contaminated poultry products intercepted by the animal quarantine service at the Japan border have been characterized in chickens and ducks, the biological properties of those H9N2 viruses in mammals remain unclear. Here, we characterized the biological features of two H9N2 virus isolates [A/chicken/Japan/AQ-HE28-50/2016 (Ck/HE28-50) and A/chicken/Japan/AQ-HE28-57/2016 (Ck/HE28-57)] in a mouse model. We found that these H9N2 viruses replicate well in the respiratory tract of infected mice without adaptation, and that Ck/HE28-57 caused body weight loss in the infected mice. Our results indicate that H9N2 avian influenza viruses isolated from raw chicken meat products illegally brought to Japan can potentially infect and cause disease in mammals.

Characterization and antiviral susceptibility of SARS-CoV-2 Omicron/BA.2.

The recent emergence of SARS-CoV-2 Omicron variants possessing large numbers of mutations has raised concerns of decreased effectiveness of current vaccines, therapeutic monoclonal antibodies, and antiviral drugs for COVID-19 against these variants1,2. While the original Omicron lineage, BA.1, has become dominant in many countries, BA.2 has been detected in at least 67 countries and has become dominant in the Philippines, India, and Denmark. Here, we evaluated the replicative ability and pathogenicity of an authentic infectious BA.2 isolate in immunocompetent and human ACE2 (hACE2)-expressing mice and hamsters. In contrast to recent data with chimeric, recombinant SARS-CoV-2 strains expressing the spike proteins of BA.1 and BA.2 on an ancestral WK-521 backbone3, we observed similar infectivity and pathogenicity in mice and hamsters between BA.2 and BA.1, and less pathogenicity compared to early SARS-CoV-2 strains. We also observed a marked and significant reduction in the neutralizing activity of plasma from COVID-19 convalescent individuals and vaccine recipients against BA.2 compared to ancestral and Delta variant strains. In addition, we found that some therapeutic monoclonal antibodies (REGN10987/REGN10933, COV2-2196/COV2-2130, and S309) and antiviral drugs (molnupiravir, nirmatrelvir, and S-217622) can restrict viral infection in the respiratory organs of hamsters infected with BA.2. These findings suggest that the replication and pathogenicity of BA.2 is comparable to that of BA.1 in rodents and that several therapeutic monoclonal antibodies and antiviral compounds are effective against Omicron/BA.2 variants.

Anti-SARS CoV-2 IgG in COVID-19 Patients with Hematological Diseases: A Single-center, Retrospective Study in Japan.

Objective Coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread globally. Although the relationship between anti-SARS-CoV-2 immunoglobulin G (IgG) antibodies and COVID-19 severity has been reported, information is lacking regarding the seropositivity of patients with particular types of diseases, including hematological diseases. Methods In this single-center, retrospective study, we compared SARS-CoV-2 IgG positivity between patients with hematological diseases and those with non-hematological diseases. Results In total, 77 adult COVID-19 patients were enrolled. Of these, 30 had hematological disorders, and 47 had non-hematological disorders. The IgG antibody against the receptor-binding domain of the spike protein was detected less frequently in patients with hematological diseases (60.0%) than in those with non-hematological diseases (91.5%; p=0.029). Rituximab use was significantly associated with seronegativity (p=0.010). Conclusion Patients with hematological diseases are less likely to develop anti-SARS-CoV-2 antibodies than those with non-hematological diseases, which may explain the poor outcomes of COVID-19 patients in this high-risk group.

Antibody titers against SARS-CoV-2 decline, but do not disappear for several months.

BACKGROUND: To develop an effective vaccine against a novel viral pathogen, it is important to understand the longitudinal antibody responses against its first infection. Here we performed a longitudinal study of antibody responses against SARS-CoV-2 in symptomatic patients. METHODS: Sequential blood samples were collected from 39 individuals at various timepoints between 0 and 154 days after onset. IgG or IgM titers to the receptor binding domain (RBD) of the S protein, the ectodomain of the S protein, and the N protein were determined by using an ELISA. Neutralizing antibody titers were measured by using a plaque reduction assay. FINDINGS: The IgG titers to the RBD of the S protein, the ectodomain of the S protein, and the N protein peaked at about 20 days after onset, gradually decreased thereafter, and were maintained for several months after onset. Extrapolation modeling analysis suggested that the IgG antibodies were maintained for this amount of time because the rate of reduction slowed after 30 days post-onset. IgM titers to the RBD decreased rapidly and disappeared in some individuals after 90 days post-onset. All patients, except one, possessed neutralizing antibodies against authentic SARS-CoV-2, which they retained at 90 days after onset. The highest antibody titers in patients with severe infections were higher than those in patients with mild or moderate infections, but the decrease in antibody titer in the severe infection cohort was more remarkable than that in the mild or moderate infection cohort. INTERPRETATION: Although the number of patients is limited, our results show that the antibody response against the first SARS-CoV-2 infection in symptomatic patients is typical of that observed in an acute viral infection. FUNDING: The Japan Agency for Medical Research and Development and the National Institutes of Allergy and Infectious Diseases.

Baloxavir Marboxil Treatment of Nude Mice Infected With Influenza A Virus.

BACKGROUND: Immunocompromised patients infected with influenza virus require prolonged treatment with neuraminidase inhibitors, because these patients are not able to eradicate the virus from the respiratory tract, leading to the emergence of drug-resistant mutant viruses. METHODS: In this study, we examined the efficacy of baloxavir marboxil in nude mice that were immunologically deficient. RESULTS: Daily treatment with a suboptimal dose of baloxavir marboxil increased the survival time of the virus-infected nude mice but did not clear the virus from their respiratory organs, resulting in gradual body weight loss after termination of treatment. CONCLUSIONS: Despite the prolonged baloxavir marboxil treatment, few resistant mutants were detected.

Influenza A variants with reduced susceptibility to baloxavir isolated from Japanese patients are fit and transmit through respiratory droplets.

Here we report the isolation of the influenza A/H1N1 2009 pandemic (A/H1N1pdm) and A/H3N2 viruses carrying an I38T mutation in the polymerase acidic protein-a mutation that confers reduced susceptibility to baloxavir marboxil-from patients before and after treatment with baloxavir marboxil in Japan. These variants showed replicative abilities and pathogenicity that is similar to those of wild-type isolates in hamsters; they also transmitted efficiently between ferrets by respiratory droplets.

Age-related immune-modulating properties of seminal fluid that control the severity of asthma are gender specific.

Reproductive organs play a pivotal role in asthma development and progression, especially in women. Endocrine environment changes associated with the menstrual cycle, pregnancy, and menopause can exacerbate the clinical features of asthma. Factors secreted by reproductive organs may be responsible for the gender difference and age-related changes in adult asthma. Here, we show that mammalian seminal fluid has anti-asthma effects exclusively in females. Exposure to murine seminal fluid markedly reduced eosinophilic airway inflammation in 2-month-old female mice upon ovalbumin inhalation. The anti-asthma effect with seminal fluid from 10-month-old males was double that with fluid from 2-month-old males, suggesting that it depended on male sexual maturation. We further found that seminal fluid from middle-aged human volunteers had beneficial effects in asthmatic female mice; these effects were associated with transcriptional repression of osteopontin and IL-17A, which are poor prognostic factors for asthma. In 2-month-old male mice, however, human seminal fluid failed to decrease asthmatic features and even enhanced osteopontin and IL-17A transcription. Our data demonstrate that age-related seminal fluid exerts opposing effects in asthmatic male and female mice. These findings may help the development of novel approaches to control the prevalence and age-related progression of asthma in women.