The omicron variant (B.1.1.529) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was the predominant variant in South Korea from late January 2022. In this study, we aimed to report the early estimates of the serial interval distribution and reproduction number to quantify the transmissibility of the omicron variant in South Korea between 25 November 2021 and 31 December 2021. We analyzed 427 local omicron cases and reconstructed 73 transmission pairs. We used a maximum likelihood estimation to assess serial interval distribution from transmission pair data and reproduction numbers from 74 local cases in the first local outbreak. We estimated that the mean serial interval was 3.78 (standard deviation, 0.76) days, which was significantly shorter in child infectors (3.0 days) compared to adult infectors (5.0 days) (p < 0.01). We estimated the mean reproduction number was 1.72 (95% CrI, 1.60–1.85) for the omicron variant during the first local outbreak. Strict adherence to public health measures, particularly in children, should be in place to reduce the transmission risk of the highly transmissible omicron variant in the community.

Background: Although nivolumab plus platinum-based chemotherapy has been approved as a first-line systemic treatment for advanced gastric cancer (AGC), the pretreatment imaging and clinical factors associated with disease progression remain incompletely understood. Methods: This retrospective study included 172 patients with AGC who underwent baseline CT and were treated with nivolumab plus chemotherapy. Factors associated with progression-free survival (PFS) were analyzed using univariable and multivariable Cox proportional hazards regression. The performance of the selected variables was evaluated using Harrell’s concordance index (C-index) and the time-dependent area under the curve (AUC). Results: Progression or death occurred in 79.1% of patients (136/172). The number of metastatic sites (hazard ratio [HR], 1.60; 95% confidence interval [CI], 1.28–1.99; p < 0.001), Eastern Cooperative Oncology Group (ECOG) performance status (PS) (HR, 2.02; 95% CI, 1.29–3.16; p = 0.003), macroscopic tumor morphology (HR, 1.69; 95% CI, 1.00–2.84; p = 0.049), and seeding score (HR, 1.16; 95% CI, 1.00–1.36; p = 0.049) were significant prognostic factors for PFS. Together, these four selected variables yielded a C-index of 0.69 (0.64–0.74) and a 12-month time-dependent AUC of 0.73 (0.66–0.81). Median PFS differed significantly between the low- and high-risk groups (9.6 months, 95% CI, 8.0–17.3 vs. 5.2 months, 95% CI, 4.1–6.6; p < 0.001). Conclusions: Combined clinical and CT imaging features, including the number of metastatic sites and ECOG PS, were independent prognostic factors for PFS in patients with AGC receiving first-line nivolumab plus chemotherapy.