Characteristics and in-hospital mortality of patients with COVID-19 from the first to fifth waves of the pandemic in 2020 and 2021 in the Japanese Medical Data Vision database.

OBJECTIVES

We aimed to describe patient characteristics, healthcare utilization, and in-hospital mortality among patients with COVID-19 in Japan across waves.

METHODS

Using a large-scale hospital-based database, we identified patients hospitalized for COVID-19 in the first (January-June 2020), second (June-October 2020), third (October 2020-February 2021), fourth (March-June 2021), and fifth (June-December 2021) waves. We summarized patient characteristics, healthcare utilization, and in-hospital mortality during each wave and performed multivariable logistic regression analyses for in-hospital mortality.

RESULTS

From the first to fifth waves, the number of patients (mean age ± standard deviation, years) was 2958 (61.2 ± 22.8), 7981 (55.6 ± 25.3), 18,788 (63.6 ± 22.9), 17,729 (60.6 ± 22.6), and 23,656 (51.2 ± 22.3), respectively. There were 190 (6.4%), 363 (4.5%), 1261 (6.7%), 1081 (6.1%), and 762 (3.2%) in-hospital deaths, respectively. The adjusted odds ratios for in-hospital deaths (95% confidence interval) were 0.78 (0.65-0.95), 0.94 (0.79-1.12), 0.99 (0.84-1.18), 0.77 (0.65-0.92), in the second to fifth waves, respectively, compared with the first wave.

CONCLUSIONS

In-hospital COVID-19 mortality improved from the first to the second wave; however, during the third and fourth waves, mortality was as serious as in the first wave. Although in-hospital mortality during the fifth wave improved, careful monitoring is needed for upcoming waves, considering changing patient and viral characteristics.