The purpose of this study was to examine epidemiology of injury in a male collegiate volleyball team in Japan during 2019 season. Thirty-six collegiate male volleyball players were followed during 2019 season. Injuries that required more than 24 hours to recover were classified as Time Loss (TL) injury, and those that required less than 24 hours were classified as Non-Time Loss (NTL) injury. Exposure was calculated by total number of players and hours of participation. Then, we computed injury rate per 1000 Player Hour (PH) and 1000 Athlete Exposure (AE) as outcome measures. A chi-square test was utilized to statistically compare. Eighteen injuries occurred and the overall injury rate was 1.28/1000PH and 2.05/1000AE, respectively. Of which, 11 cases were NTL injuries (0.78/1000PH, 1.26/1000AE) and 7 cases were TL injuries (0.50/1000PH, 0.80/1000AE). Within the 7 TL injuries, 5 (0.36/1000PH, 0.57/1000AE) were of minor severity. Most TL injury were classified as chronic in nature (n=5, 0.36/1000PH, 0.57/1000AE). There was no statistically significant difference between injury rate of match (n=2, 1.33/1000PH, 2.88/1000AE) and training (n=16, 1.27/1000PH, 1.98/1000AE). The most frequently injured body part in training was lower back (n=7, 0.56/1000PH, 0.87/1000AE). In match, highest injury rate was observed in ankle (n=2, 1.33/1000PH, 2.88/1000AE). In conclusion, our results showed relatively low injury rate, and majority of reported injuries were categorized as minor severity. Our study also demonstrated injury characteristics of Japanese male collegiate players that lower back injuries were prevalent in training, and acute ankle injury rate was highest in match.

Objective: Monitoring the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants is important due to concerns regarding infectivity, transmissibility, immune evasion and disease severity. We evaluated the temporal and regional replacement of previous SARS-CoV-2 variants by the emergent strains, Alpha and Delta. Methods: We obtained the results of polymerase chain reaction screening tests for variants conducted in multiple commercial laboratories. Assuming that all previous strains would be replaced by one variant, the new variant detection rate was estimated by fitting a logistic growth model. We estimated the transmission advantage of each new variant over the pre-existing virus strains. Results: The variant with the N501Y mutation was first identified in the Kinki region in early February 2021, and by early May, it had replaced more than 90% of the previous strains. The variant with the L452R mutation was first detected in the Kanto-Koshin region in mid-May, and by early August, it comprised more than 90% of the circulating strains. Compared with pre-existing strains, the variant with the N501Y mutation showed transmission advantages of 48.2% and 40.3% in the Kanto-Koshin and Kinki regions, respectively, while the variant with the L452R mutation showed transmission advantages of 60.1% and 71.9%, respectively. Discussion In Japan, Alpha and Delta variants displayed regional differences in the replacement timing and their relative transmission advantages. Our method is efficient in monitoring and estimating changes in the proportion of variant strains in a timely manner in each region.