Protection of Omicron Bivalent Vaccine, Previous Infection, and Their Induced Neutralizing Antibodies Against Symptomatic Infection With Omicron XBB.1.16 and EG.5.1.

Background: Data are limited on the protective role of the Omicron BA bivalent vaccine, previous infection, and their induced neutralizing antibodies against Omicron XBB.1.16 and EG.5.1 infection. Methods: We conducted a nested case-control analysis among tertiary hospital staff in Tokyo who had received ≥3 doses of COVID-19 vaccines and donated blood samples in June 2023 (1 month before the Omicron XBB.1.16 and EG.5.1 wave). We identified 206 symptomatic cases between June and September 2023 and selected their controls with 1:1 propensity score matching. We examined the association of vaccination, previous infection, and preinfection live virus neutralizing antibody titers against Omicron XBB.1.16 and EG.5.1 with the risk of COVID-19 infection. Results: Previous infection during the Omicron BA- or XBB-dominant phase was associated with a significantly lower infection risk during the XBB.1.16 and EG.5.1-dominant phase than infection-naive status, with 70% and 100% protection, respectively, whereas Omicron BA bivalent vaccination showed no association. Preinfection neutralizing titers against XBB.1.16 and EG.5.1 were 39% (95% CI, 8%-60%) and 28% (95% CI, 8%-44%) lower in cases than matched controls. Neutralizing activity against XBB.1.16 and EG.5.1 was somewhat detectable in the sera of individuals with previous infection but barely detectable in those who were infection naive and received the Omicron bivalent vaccine. Conclusions: In the era when the Omicron XBB vaccine was unavailable, the Omicron BA bivalent vaccine did not confer the neutralizing activity and protection against Omicron XBB.1.16 and EG.5.1 symptomatic infection. The previous infection afforded neutralizing titers and protection against symptomatic infection with these variants.

Correlates of Nucleocapsid Antibodies and a Combination of Spike and Nucleocapsid Antibodies Against Protection of SARS-CoV-2 Infection During the Omicron XBB.1.16/EG.5-Predominant Wave.

Background: We aimed to examine the association among nucleocapsid (N) antibodies, a combination of N and spike (S) antibodies, and protection against SARS-CoV-2 reinfection. Methods: We conducted a prospective cohort study among staff at a national medical research center in Tokyo and followed them for the incidence of SARS-CoV-2 infection between June and September 2023 (Omicron XBB.1.16/EG.5 wave). At baseline, participants donated blood samples to measure N- and S-specific antibodies. Cox regression was used to estimate the hazard ratio and protection ([1 - hazard ratio] × 100) against subsequent SARS-CoV-2 infection across these antibody levels. Results: Among participants with previous infection, higher pre-reinfection N antibodies were associated with a lower risk of reinfection, even after adjusting S antibody levels (P < .01 for trend). Estimation of the protection matrix for N and S antibodies revealed that high levels in N and S antibodies conferred robust protection (>90%) against subsequent infection. In addition, a pattern of low pre-reinfection N antibodies but high vaccine-enhanced S antibodies showed high protection (>80%). Conclusions: Pre-reinfection N antibody levels correlated with protection against reinfection, independent of S antibodies. If the N antibodies were low, vaccine-boosted S antibodies might enhance the reinfection protection.

A Case of Spinal Echinococcosis in a Japanese Woman Living in Tokyo: Diagnostic Challenges in Non-endemic Areas and Public Health Implications.

Echinococcosis, caused by Echinococcus spp., often affects the lungs and liver, and spinal involvement is rare. Echinococcus multilocularis is prevalent in Japan, particularly in Hokkaido. We herein report a rare case of spinal echinococcosis in a 31-year-old woman who was diagnosed in Tokyo. Spinal echinococcosis is uncommon and often leads to misdiagnoses. The patient likely contracted the disease via contaminated fresh produce transported from an endemic region. This study emphasizes the diagnostic challenges of spinal echinococcosis in non-endemic regions and highlights the public health concerns related to the spread of infections in non-endemic areas.

Blood perfusion with polymyxin B immobilized columns in patients with COVID-19 requiring oxygen therapy.

Extracorporeal blood purification with polymyxin B immobilized fiber column direct hemoperfusion (PMX-DHP), is reported to be effective in treating COVID-19 pneumonitis with oxygen demand. This multicenter prospective study evaluated the efficacy and safety of PMX-DHP in oxygen-requiring patients with COVID-19 admitted between September 28, 2020, and March 31, 2022. The primary endpoint was the percentage of clinical improvement 15 days after treatment. The secondary endpoint was the percentage of worsened disease status. Data from the COVID-19 patient registry were used for the synthetic control group. The improvement rate on Day 15 did not differ between PMX-treated patients and controls; however, the deterioration rate was 0.38 times lower in the PMX-treated group, and the death rates on Day 29 were 0 and 11.1% in the PMX-treated and control groups, respectively. The PMX group showed a 0.73 times higher likelihood for reduced intensive care demand, as 16.7% of PMX-treated patients and 22.8% of controls worsened. After treatment blood oxygenation improved, urinary ß2-microglobulin and liver-type fatty acid-binding protein showed significant decreases, and IL-6 decreased once during treatment but did not persist. In this study, PMX treatment effectively prevented the worsening of COVID-19 pathology, accompanied by improved oxygenation. PMX treatment to remove activated cells may effectively improve patient outcomes.

Vitamin D deficiency during the coronavirus disease 2019 (COVID-19) pandemic among healthcare workers.

BACKGROUND & AIMS: Vitamin D deficiency is a common nutritional problem worldwide that may have worsened during the coronavirus disease 2019 (COVID-19) pandemic. The present study sought to examine the prevalence and correlates of vitamin D deficiency among healthcare workers three years after the start of the COVID-19 pandemic. METHODS: Participants comprised 2543 staff members from a medical research institute, who completed a questionnaire and donated blood samples in June 2023. 25-hydroxyvitamin D (25[OH]D) levels were measured using an electrochemiluminescence immunoassay. Logistic regression was used to calculate the odds ratio and its 95% confidence interval while adjusting for covariates. RESULTS: The proportions of participants with vitamin D insufficiency (25[OH]D 20-29 ng/mL) and deficiency (25[OH]D < 20 ng/mL) were 44.9% and 45.9%, respectively. In a multivariable-adjusted model, factors associated with a higher prevalence of vitamin D deficiency included younger age, female sex, fewer hours of daytime outdoor physical activity during leisure time (without regular use of sunscreen), lower intake of fatty fish, no use of vitamin D supplements, smoking, and no alcohol consumption. Occupational factors, including shift work, were not independently associated with vitamin D deficiency. CONCLUSIONS: Our results suggest that vitamin D insufficiency and deficiency are highly prevalent among healthcare workers. Health education regarding lifestyle modifications for this occupational group are warranted to improve their vitamin D status in the COVID-19 era.

Clinical trends among patients with asthma hospitalized for COVID-19 based on data from a nationwide database: an observational study.

BACKGROUND: While the prevalence of severe cases and mortality rate of coronavirus disease 2019 (COVID-19) appear to be reducing, the clinical characteristics and severity of hospitalized patients with asthma and COVID-19 remain largely unknown. This study aimed to examine the association of asthma with COVID-19 severity and mortality risk. METHODS: Data from the Japanese COVID-19 Registry Database were used to investigate the association between COVID-19 and asthma. This study focused on patients hospitalized for COVID-19 in 690 facilities from January 31, 2020, to December 31, 2022. Multivariate analysis using logistic regression was conducted to assess whether asthma, compared with other conditions, represents a risk factor for mortality and invasive mechanical ventilation after COVID-19. RESULTS: In total, 72,582 patients with COVID-19 were included in the analysis, of whom, 3731 were diagnosed with asthma. From January 2020 to June 2021, asthma showed no significant association with an increase in mortality (OR 0.837, 95% CI 0.639-1.080, p = 0.184) or invasive mechanical ventilation events (OR 1.084, 95% CI 0.878-1.326, p = 0.440). An analysis conducted after July 2021 yielded similar results. For patients with asthma, factors such as age, body-mass index, sex, and chronic kidney disease increased the risk of mechanical ventilation. However, non-vaccination status and high blood pressure increased the risk of mechanical ventilation during the second half of the study. CONCLUSION: Patients with asthma did not have an increased risk of mortality or mechanical ventilation due to COVID-19. However, patients with asthma had a higher risk of more severe COVID-19 due to factors such as advancing age, elevated body-mass index, chronic kidney disease, and non-vaccination.

Diagnostic accuracy of direct reverse transcription-polymerase chain reaction using guanidine-based and guanidine-free inactivators for SARS-CoV-2 detection in saliva samples.

This study aimed to evaluate diagnostic accuracy of SARS-CoV-2 RNA detection in saliva samples treated with a guanidine-based or guanidine-free inactivator, using nasopharyngeal swab samples (NPS) as referents. Based on the NPS reverse transcription-polymerase chain reaction (RT-PCR) results, participants were classified as with or without COVID-19. Fifty sets of samples comprising NPS, self-collected raw saliva, and saliva with a guanidine-based, and guanidine-free inactivator were collected from each group. In patients with COVID-19, the sensitivity of direct RT-PCR using raw saliva and saliva treated with a guanidine-based and guanidine-free inactivator was 100.0%, 65.9%, and 82.9%, respectively, with corresponding concordance rates of 94.3% (κ=88.5), 82.8% (κ=64.8), and 92.0% (κ=83.7). Among patients with a PCR Ct value of <30 in the NPS sample, the positive predictive value for the three samples was 100.0%, 80.0%, and 96.0%, respectively. The sensitivity of SARS-CoV-2 RNA detection was lower in inactivated saliva than in raw saliva and lower in samples treated with a guanidine-based than with a guanidine-free inactivator. However, in individuals contributing to infection spread, inactivated saliva showed adequate accuracy regardless of the inactivator used. Inactivators can be added to saliva samples collected for RT-PCR to reduce viral transmission risk while maintaining adequate diagnostic accuracy.

Inhaled ciclesonide does not affect production of antibodies or elimination of virus in patients with COVID-19: Subanalysis of a multicenter, open-label randomized trial.

During an earlier multicenter, open-label, randomized controlled trial designed to evaluate the effectiveness of high-dose inhaled ciclesonide in patients with asymptomatic or mild coronavirus disease 2019 (COVID-19), we observed that worsening of shadows on CT without worsening of clinical symptoms was more common with ciclesonide. The present study sought to determine if an association exists between worsening CT shadows and impaired antibody production in patients treated with inhaled ciclesonide. Eighty-nine of the 90 patients in the original study were prospectively enrolled. After exclusions, there were 36 patients each in the ciclesonide and control groups. We analyzed antibody titers against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein at various time points. Changes in viral load during treatment were compared. There was no significant difference in age, sex, body mass index, background clinical characteristics, or symptoms between the two groups. Although evaluation on day 8 suggested a greater tendency for worsening shadows on CT in the ciclesonide group (p = 0.072), there was no significant difference between them in the ability to produce antibodies (p = 0.379) or the maximum antibody titer during the clinical course. In both groups, worsening CT shadows and higher viral loads were observed on days 1-8, suggesting ciclesonide does not affect clearance of the virus (p = 0.134). High-dose inhaled ciclesonide did not impair production of antibodies against SARS-CoV-2 or affect elimination of the virus, suggesting that this treatment can be used safely in patients with COVID-19 patients who use inhaled steroids for asthma and other diseases.

Preinfection Neutralizing Antibodies, Omicron BA.5 Breakthrough Infection, and Long COVID: A Propensity Score-Matched Analysis.

BACKGROUND: Data are limited on the role of preinfection humoral immunity protection against Omicron BA.5 infection and long coronavirus disease (COVID) development. METHODS: We conducted nested case-control analysis among tertiary hospital staff in Tokyo who donated blood samples in June 2022 (1 month before Omicron BA.5 wave), approximately 6 months after receiving a third dose of COVID-19 mRNA vaccine. We measured live virus-neutralizing antibody titers against wild type and Omicron BA.5, and anti-receptor-binding domain (RBD) antibody titers at preinfection, and compared them between cases and propensity-matched controls. Among the breakthrough cases, we examined association between preinfection antibody titers and incidence of long COVID. RESULTS: Preinfection anti-RBD and neutralizing antibody titers were lower in cases than controls. Neutralizing titers against wild type and Omicron BA.5 were 64% (95% confidence interval [CI], 42%-77%) and 72% (95% CI, 53%-83%) lower, respectively, in cases than controls. Individuals with previous Omicron BA.1/BA.2 infections were more frequent among controls than cases (10.3% vs 0.8%), and their Omicron BA.5 neutralizing titers were 12.8-fold higher than infection-naive individuals. Among cases, preinfection antibody titers were not associated with incidence of long COVID. CONCLUSIONS: Preinfection immunogenicity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may play a role in protecting against the Omicron BA.5 infection but not preventing long COVID.

Carboplatin and weekly paclitaxel in combination with bevacizumab for the treatment of advanced non-small cell lung cancer complicated by idiopathic interstitial pneumonias: A feasibility study.

BACKGROUND: Idiopathic interstitial pneumonias are an independent risk factor of lung cancer, and a chemotherapy-induced acute exacerbation is the most common lethal complication in Japanese patients. The safety and efficacy of carboplatin and weekly paclitaxel for the treatment of non-small cell lung cancer with idiopathic interstitial pneumonias has been previously reported in prospective studies. However, carboplatin + paclitaxel with bevacizumab is currently the standard therapy. We conducted a multicenter, phase II study to confirm the safety and efficacy of carboplatin + weekly paclitaxel + bevacizumab for the treatment of patients with lung cancer complicated by idiopathic interstitial pneumonias. METHODS: Chemotherapy-naïve patients with advanced-stage or patients with post-operative recurrent non-squamous non-small cell lung cancer complicated by idiopathic interstitial pneumonias were enrolled. Patients received carboplatin (area under the curve: 5.0) and bevacizumab (15 mg/kg) on day 1 and paclitaxel (100 mg/m2) on days 1, 8, and 15 of each 4-week cycle. RESULTS: Seventeen patients less than the predetermined number were enrolled and received a median of four treatment cycles (range: 1-6). One patient (5.9%; 95% confidence interval: 0.1-28.7%) had acute exacerbation of interstitial pneumonia related to the study treatment which improved after corticosteroid treatment. The overall response rate was 52.9%. The median progression-free survival, median survival time, and 1-year survival were 5.7 months, 12.9 months, and 52.9%, respectively. CONCLUSION: The addition of bevacizumab to carboplatin and weekly paclitaxel might be safe and effective for the treatment of advanced non-small cell lung cancer complicated by idiopathic interstitial pneumonias. CLINICAL TRIAL REGISTRATION NUMBER: UMIN000008189.

Durability and determinants of anti-SARS-CoV-2 spike antibodies following the second and third doses of mRNA COVID-19 vaccine.

OBJECTIVES: To examine the differences in durability and its determinants of humoral immunity following 2- and 3-dose COVID-19 vaccination. METHODS: Throughout the pandemic, we evaluated the anti-spike IgG antibody titers of 2- and 3-dose mRNA vaccine recipients over time among the staff of a medical and research center in Tokyo. Linear mixed models were used to estimate trajectories of antibody titers from 14 to 180 days after the last immune-conferred event (vaccination or infection) and compare antibody waning rates across prior infection and vaccination status, and across background factors in infection-naïve participants. RESULTS: A total of 6901 measurements from 2964 participants (median age, 35 years; 30% male) were analyzed. Antibody waning rate (percentage per 30 days [95% CI]) was slower after 3 doses (25% [23-26]) than 2 doses (36% [35-37]). Participants with hybrid immunity (vaccination and infection) had further slower waning rates: 2-dose plus infection (16% [9-22]); 3-dose plus infection (21% [17-25]). Older age, male sex, obesity, coexisting diseases, immunosuppressant use, smoking, and alcohol drinking were associated with lower antibody titers, whereas these associations disappeared after 3 doses, except for sex (lower in female participants) and immunosuppressant use. Antibody waned slightly faster in older participants, females, and alcohol drinkers after 2 doses, whereas it did not differ after 3 doses across except sex. DISCUSSION: The 3-dose mRNA vaccine conferred higher durable antibody titers, and previous infection modestly enhanced its durability. The antibody levels at a given time point and waning speed after 2 doses differed across background factors; however, these differences mostly diminished after 3 doses.

Omicron BA.1 neutralizing antibody response following Delta breakthrough infection compared with booster vaccination of BNT162b2.

BACKGROUND: Longitudinal data are lacking to compare booster effects of Delta breakthrough infection versus third vaccine dose on neutralizing antibodies (NAb) against Omicron. METHODS: Participants were the staff of a national research and medical institution in Tokyo who attended serological surveys on June 2021 (baseline) and December 2021 (follow-up); in between, the Delta-dominant epidemic occurred. Of 844 participants who were infection-naïve and had received two doses of BNT162b2 at baseline, we identified 11 breakthrough infections during follow-up. One control matched to each case was selected from boosted and unboosted individuals. We compared live-virus NAb against Wild-type, Delta, and Omicron BA.1 across groups. RESULTS: Breakthrough infection cases showed marked increases in NAb titers against Wild-type (4.1-fold) and Delta (5.5-fold), and 64% had detectable NAb against Omicron BA.1 at follow-up, although the NAb against Omicron after breakthrough infection was 6.7- and 5.2-fold lower than Wild-type and Delta, respectively. The increase was apparent only in symptomatic cases and as high as in the third vaccine recipients. CONCLUSIONS: Symptomatic Delta breakthrough infection increased NAb against Wild-type, Delta, and Omicron BA.1, similar to the third vaccine. Given the much lower NAb against Omicron BA.1, infection prevention measures must be continued irrespective of vaccine and infection history while the immune evasive variants are circulating.

Diagnosis of diffuse panbronchiolitis by transbronchial lung cryobiopsy.

A 70-year-old man began to cough. Chest X-ray showed a tumor in the center, pleural effusion on the left side, and diffuse granular shadows on the right side. Chest computed tomography (CT) showed bronchial wall thickening and numerous granular shadows. We suspected diffuse panbronchiolitis. Thus, transbronchial lung biopsy (TBLB) and transbronchial lung cryobiopsy (TBLC) were performed. The tissue size obtained was 1 mm by TBLB and 6 mm at 5 seconds by TBLC. Histological analysis of the TBLB specimen showed lymphocyte infiltration, no fibrosis in Hematoxylin-eosin (HE) staining, and no elastic fibers in Elastica van Gieson (EVG) staining. On the other hand, TBLC specimens showed inflammatory cell infiltration and fibrosis around the bronchioles in HE staining and hypertrophy of elastic fibers in EVG staining. It was diagnosed as diffuse panbronchiolitis (DPB) from clinical and pathological findings. Cryobiopsy is useful in diagnosing DPB as well as interstitial pneumonia and lung cancer.

Urinary L-Type Fatty Acid-Binding Protein Predicts Oxygen Demand of COVID-19 in Initially Mild Cases.

Early detection of illness trajectory in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infected patients is crucial for patients and healthcare workers. An effective, noninvasive approach, with simple measurement for decision-making, is necessary in a pandemic to discriminate between high- and low-risk patients, even though both groups may exhibit mild symptoms in the beginning. OBJECTIVES: To predict COVID-19 disease severity within 10 days, distinguishing cases that will progress to moderate or severe versus mild, patient urinary L-type fatty acid-binding protein (L-FABP) was assayed within 4 days of receiving a diagnosis. The study also examined whether L-FABP point of care (POC) test is helpful in risk screening. DESIGN: Symptomatic subjects who tested positive for SARS-CoV-2 and were hospitalized were prospectively enrolled at the National Center for Global Health and Medicine (NCGM), Yamanashi Prefectural Central Hospital (YPCH), and Sinai Hospital in Maryland. The outcome of each case was evaluated 7 days after admission and the diagnostic performance of L-FABP was assessed. SETTING AND PARTICIPANTS: Subjects were treated for COVID-19 at public healthcare centers in Japan from January 31, 2020, to January 31, 2021, to NCGM, YPCH, and at Sinai Hospital in Baltimore, MD, during the same period. MAIN OUTCOMES AND MEASURES: The primary outcome was to determine whether urinary L-FABP within 48 hours of admission can predict the patient's severity of COVID-19 1 week later. We obtained demographic data, information on clinical symptoms, radiographic images, and laboratory data. RESULTS: Diagnostic performance was assessed using receiver operating characteristic analysis. Of the 224 participants in the study, 173 initially had a mild form of COVID-19. The area under the curve (AUC) for a severe outcome was 93.5%. L-FABP POC risk prediction of a severe outcome had an AUC of 88.9%. CONCLUSIONS AND RELEVANCE: Urinary L-FABP can predict patient risk of COVID-19 illness severity. L-FABP POC is implementable for patient management. (ClinicalTrials.gov number, NCT04681040).

Examination of the utility of the COVID-19 detection kit, TRC Ready® SARS-CoV-2 i for nasopharyngeal swabs.

The reverse transcription polymerase chain reaction (RT-PCR) offers high sensitivity, but has some drawbacks, such as the time required for the RNA extraction. Transcription reverse-transcription concerted reaction (TRC) Ready® SARS-CoV-2 i is easy to use and can be performed in about 40 minutes. TRC Ready® SARS-CoV-2 i and real-time one-step RT-PCR using the TaqMan probe tests of cryopreserved nasopharyngeal swab samples from patients diagnosed with COVID-19 were compared. The primary objective was to examine the positive and negative concordance rates. A total of 69 samples cryopreserved at -80° C were examined. Of the 37 frozen samples that were expected to be RT-PCR positive, 35 were positive by the RT-PCR method. TRC Ready® SARS-CoV-2 i detected 33 positive cases and 2 negative cases. One frozen sample that was expected to be RT-PCR positive was negative on both TRC Ready® SARS-CoV-2 i and RT-PCR. In addition, one frozen sample that was expected to be RT-PCR positive was positive by the RT-PCR method and negative by TRC Ready® SARS-CoV-2 i. Of the 32 frozen samples that were expected to be RT-PCR negative, both the RT-PCR method and TRC Ready® SARS-CoV-2 i yielded negative results for all 32 samples. Compared with RT-PCR, TRC Ready® SARS-CoV-2 i had a positive concordance rate of 94.3% and a negative concordance rate of 97.1%. TRC Ready® SARS-CoV-2 i can be utilized in a wide range of medical sites such as clinics and community hospitals due to its ease of operability, and is expected to be useful in infection control.

High-flow nasal cannula for severe COVID-19 patients in a Japanese single-center, retrospective, observational study: 1 year of clinical experience.

High-flow nasal cannula (HFNC) can be effective in treating type 1 respiratory failure by reducing the severity of coronavirus disease 2019 (COVID-19). The purpose of this study was to assess the reduction of disease severity and safety of HFNC treatment in patients with severe COVID-19. We retrospectively observed 513 consecutive patients with COVID-19 admitted to our hospital from January 2020 to January 2021. We included patients with severe COVID-19 who received HFNC for their deteriorating respiratory status. HFNC success was defined as improvement in respiratory status after HFNC and transfer to conventional oxygen therapy, while HFNC failure was defined as transfer to non-invasive positive pressure ventilation or ventilator, or death after HFNC. Predictive factors associated with failure to prevent severe disease were identified. Thirty-eight patients received HFNC. Twenty-five (65.8%) patients were classified in the HFNC success group. In the univariate analysis, age, history of chronic kidney disease (CKD), non-respiratory sequential organ failure assessment (SOFA) ≥ 1, oxygen saturation to fraction of inspired oxygen ratio (SpO2/FiO2) before HFNC ≤ 169.2, were significant predictors of HFNC failure. Multivariate analysis revealed that SpO2/FiO2 value before HFNC ≤ 169.2 was an independent predictor of HFNC failure. No apparent nosocomial infection occurred during the study period. Appropriate use of HFNC for acute respiratory failure caused by COVID-19 can reduce the severity of severe disease without causing nosocomial infection. Age, history of CKD, non-respiratory SOFA before HFNC ≤ 1, and SpO2/FiO2 before HFNC ≤ 169.2 were associated with HFNC failure.

Cumulative and undiagnosed SARS-CoV-2 infection among the staff of a medical research centre in Tokyo after the emergence of variants.

To describe the trend of cumulative incidence of coronavirus disease 19 (COVID-19) and undiagnosed cases over the pandemic through the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants among healthcare workers in Tokyo, we analysed data of repeated serological surveys and in-house COVID-19 registry among the staff of National Center for Global Health and Medicine. Participants were asked to donate venous blood and complete a survey questionnaire about COVID-19 diagnosis and vaccine. Positive serology was defined as being positive on Roche or Abbott assay against SARS-CoV-2 nucleocapsid protein, and cumulative infection was defined as either being seropositive or having a history of COVID-19. Cumulative infection has increased from 2.0% in June 2021 (pre-Delta) to 5.3% in December 2021 (post-Delta). After the emergence of the Omicron, it has increased substantially during 2022 (16.9% in June and 39.0% in December). As of December 2022, 30% of those who were infected in the past were not aware of their infection. Results indicate that SARS-CoV-2 infection has rapidly expanded during the Omicron-variant epidemic among healthcare workers in Tokyo and that a sizable number of infections were undiagnosed.

Neutralizing antibodies after three doses of the BNT162b2 vaccine, breakthrough infection, and symptoms during the Omicron-predominant wave.

OBJECTIVES: To investigate the role of immunogenicity after the third vaccine dose against Omicron infection and COVID-19-compatible symptoms of infection. METHODS: First, we examined vaccine effectiveness (VE) of the third dose against the second dose during the Omicron wave among the staff at a tertiary hospital in Tokyo. In a case-control study of third vaccine recipients, we compared the preinfection live-virus neutralizing antibodies (NAb) against Omicron between breakthrough cases and their controls who had close contact with patients with COVID-19. Among these cases, we examined the association between NAb levels and the number of COVID-19-compatible symptoms. RESULTS: Among the 1456 participants for VE analysis, 60 breakthrough infections occurred during the Omicron wave. The third dose VE for infection was 54.6%. Among the third dose recipients, NAb levels against Omicron did not differ between the cases (n = 22) and controls (n = 21). Among the cases, those who experienced COVID-19-compatible symptoms had lower NAb levels against Omicron than those who did not. CONCLUSION: The third vaccine dose was effective in decreasing the risk of SARS-CoV-2 infection during Omicron wave compared with the second dose. Among third dose recipients, higher preinfection NAb levels may not be associated with a lower risk of Omicron infection. Contrarily, they may be associated with fewer symptoms of infection.