COVID-19-Related Symptoms during the SARS-CoV-2 Omicron (B.1.1.529) Variant Surge in Japan.

The exact profiles of the clinical symptoms related to the SARS-CoV-2 Omicron variant (B.1.1.529) remain largely uncertain. Therefore, this study aimed to clarify the clinical manifestations of infection with this variant. We enrolled individuals who were tested by quantitative nasopharyngeal swab reverse transcription-polymerase chain reaction (RT-PCR) test at a large screening center in a city of Japan during the B.1.1.529 Omicron variant wave between January and May 2022, after contact with COVID-19 patients. Swab tests were planned to be performed approximately 4-5 days after contact. The presence of COVID-19-related symptoms was assessed at the swab test site. Among the 2,507 enrolled individuals, 943 (37.6%) were RT-PCR test-positive and 1,564 (62.4%) were test-negative. Among the 943 PCR test-positive participants, the prevalence of the symptoms was as follows: 47.3% with cough, 32.9% with sore throat, 18.4% with fatigability, 12.7% with fever of ≥ 37.5℃, 9.9% with dyspnea, 2.1% with dysosmia, and 1.4% with dysgeusia. The prevalence of cough, sore throat, dyspnea, and fatigability was higher among adults aged ≥ 18 years than among children and adolescents. The prevalence of dysosmia and dysgeusia remarkably decreased during the Omicron wave (1-3%) compared to during the pre-Omicron variant waves (15-25%). In summary, common COVID-19-related symptoms during the Omicron variant wave included cough and sore throat, followed by fatigability, fever, and dyspnea. The prevalence of most of these symptoms was higher in adults than in non-adults. The prevalence of dysosmia and dysgeusia remarkably decreased with the Omicron variant than with pre-Omicron variants.

Effectiveness of third vaccine dose for coronavirus disease 2019 during the Omicron variant pandemic: a prospective observational study in Japan.

The administration of a third booster dose of messenger ribonucleic acid (mRNA) vaccines against coronavirus disease 2019 (COVID-19) has progressed worldwide. Since January 2022, Japan has faced a nationwide outbreak caused by the Omicron variant, which occurred simultaneously with the progression of mass vaccination with the third booster dose. Therefore, this study evaluated the effectiveness of the third dose of vaccine by reverse transcription-polymerase chain reaction (RT-PCR) test using nasopharyngeal swab samples from adults aged ≥ 18 years tested after having close contact with COVID-19 cases between January and May 2022. Participants who completed only one dose were excluded from the study. Among the 928 enrolled participants, 139 had never been vaccinated, 609 had completed two doses, 180 had completed three doses before the swab test, and the overall RT-PCR test positivity rate in each group was 48.9%, 46.0%, and 32.2%, respectively. The vaccine effectiveness of the third dose to prevent infection after close contact was approximately 40% (95% confidence interval: 20-60%), which was the highest at 10-70 days after receiving the third dose. In conclusion, the effectiveness of the three-dose mRNA COVID-19 vaccine after close contact during the Omicron outbreak is approximately 40%.

COVID-19 Transmission at Schools in Japan.

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a global public health concern in 2021. However, the risk of attending schools during the pandemic remains unevaluated. This study estimated the secondary transmission rate at schools using the results of a real-time reverse transcription-polymerase chain reaction (RT-PCR) screening test performed between July 2020 and April 2021, before starting the nationwide mass vaccination. A total of 1,924 students (20 RT-PCR-positive; 1.0%) from 52 schools or preschools were evaluated, together with 1,379 non-adults (95 RT-PCR-positive; 6.9%) exposed to SARS-CoV-2 in non-school environments. Assuming that the infectious index cases were asymptomatic and the transmission at schools followed a Bernoulli process, we estimated the probability of transmission after each contact at school as approximately 0.005 (0.5% per contact) with the current infection prevention measures at schools in Japan (i.e., hand hygiene, physical distancing, wearing masks, and effective ventilation). Furthermore, assuming that all children are capable of carrying the infection, then contact between an index case and 20-30 students per day at schools would yield the expected value for secondary cases of ≥ 1.0, during the 10 days of the infectious period. In conclusion, with the current infection prevention measures at schools in Japan, secondary transmission at schools would occur in approximately every 200 contacts. When considering this rate, compliance with the current infection prevention measures at schools and early detection and quarantine of the index cases would be effective in preventing the spread of COVID-19 at schools.

Impacts of Natural Environmental Factors and Prevalence of Airway Symptoms on the Local Spread of COVID-19: A Time-Series Analysis in Regional COVID-19 Epidemics.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is the world's largest public health concern in 2021. This study evaluated the associations of the prevalence of airway symptoms among the tested individuals and data regarding the natural environmental factors with the weekly number of newly diagnosed COVID-19 patients in Sendai City (Nt). For the derivatives of the screening test results, data from individuals with a contact history who underwent nasopharyngeal swab reverse transcription-polymerase chain reaction (RT-PCR) testing between July 2020 and April 2021 (6,156 participants, including 550 test-positive patients) were used. The value of Nt correlated with the weekly RT-PCR test-positive rate after close contact, prevalence of cough symptoms in test-positive individuals or in test-negative individuals, lower air temperature, lower air humidity, and higher wind speed. The weekly test-positive rate correlated with lower air humidity and higher wind speed. In cross-correlation analyses, natural environmental factors correlated with the regional epidemic status on a scale of months, whereas the airway symptoms among non-COVID-19 population affected on a scale of weeks. When applying an autoregression model to the serial data of Nt, large-scale movements of people were suggested to be another factor to influence the local epidemics on a scale of days. In conclusion, the prevalence of cough symptoms in the local population, lower air humidity or higher wind speed, and large-scale movements of people in the locality would jointly influence the local epidemic status of COVID-19.