ABSTRACT
Objective Just before the Tokyo 2020 Olympic and Paralympic Games in Japan, the number of people infected with coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), started to increase at an unprecedented rate. This study investigated the effectiveness of vaccines in large-scale sporting events under difficult circumstances, such as during adherence to a bubble system and confinement inside the Olympic/Paralympic Village. Methods In collaboration with medical clinics inside and outside the Village, a prospective cohort study was conducted among overseas participants using the results of polymerase chain reaction (PCR) tests for SARS-CoV-2 upon leaving Japan. Results A total of 12,072 foreign participants were enrolled, 13 (0.11%) of whom had a positive PCR test result. None of these cases were broadcasters or members of the press, were tested outside the Olympic Village, or had a history of COVID-19 infection. The effectiveness of full vaccination and vaccination at least once (≥14 days ago) was 74% (95% confidence interval [CI]: 6-93%) and 81% (95% CI: 30-95%), respectively. Three breakthrough infections with the Delta variant were observed in 6,485 fully vaccinated participants (0.05%). The positivity rate was 0.09% among adherents to the bubble system and 0.28% among non-adherents, but this difference was not significant. Conclusion These findings indicate that even huge sporting events such as the Olympic and Paralympic Games can proceed while pandemics are ongoing in the host country by combining countermeasures such as vaccination, frequent testing, social distancing, and adherence to a bubble system.
ABSTRACT
In the coronavirus disease 2019 (COVID-19) pandemic, more than half of the cases of transmission may occur via asymptomatic individuals, which makes it difficult to contain. However, whether viral load in the throat during admission is different between asymptomatic and symptomatic patients is not well known. By conducting a prospective cohort study of patients with asymptomatic or mild COVID-19, cycle threshold (Ct) values of the polymerase chain reaction test for COVID-19 were examined every other day during admission. The Ct values during admission increased more steadily in symptomatic patients and febrile patients than in asymptomatic patients, with significance (p = 0.01 and p = 0.004, respectively), although the Ct values as a whole were not significantly different between the two groups. Moreover, the Ct values as a whole were higher in patients with dysosmia/dysgeusia than in those without it (p = 0.02), whereas they were lower in patients with a headache than those without (p = 0.01). Patients who were IgG-positive at discharge maintained higher Ct values, e.g., more than 35, during admission than those with IgG-negative (p = 0.03). Assuming that viral load and Ct values are negatively associated, the viral loads as a whole and their changes by time may be different by symptoms and immune reaction, i.e., IgG-positive at discharge.