The continued impact of COVID-19 during the Omicron era on immunocompromised individuals in Japan.

BACKGROUND

Under Japan's Infectious Disease Act, coronavirus disease-2019 (COVID-19) was reclassified from a category II to a category V infectious disease, changing it from a notifiable disease to a sentinel disease within the surveillance system given the reduced risk of severe outcomes since the Omicron era. However, the COVID-19 disease burden in immunocompromised (IC) individuals during and after the Omicron era has not been sufficiently examined.

OBJECTIVES

The COVID-19 disease burden during and after the Omicron era in IC individuals in Japan was investigated.

METHODS

This retrospective observational study used an insurance claims database. The baseline period was January 2018-December 2022; the study follow-up period was January 2023-December 2023, which coincided with the Omicron era. Adjusted incidence rate ratios (aIRRs) for COVID-19 related hospitalization, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, COVID-19 related intensive care unit (ICU) admission, and COVID-19 related death in IC individuals (vs non-IC individuals) were calculated using Poisson regression models.

RESULTS

Data were analyzed for 3,433,430 individuals, including 179,268 IC individuals. The aIRR (95 % confidence interval [CI]) values for hospitalization, SARS-CoV-2 infection, ICU admission, and death were 2.60 (2.47-2.74), 1.12 (1.09-1.15), 2.94 (2.54-3.39), and 3.34 (3.07-3.65), respectively. Among IC individuals who had B cell-depleting therapy, solid organ transplantation, and hematologic malignancies, the aIRR (95 % CI) values for hospitalization were 5.10 (4.19-6.22), 4.00 (0.56-28.40), and 3.03 (2.65-3.45), respectively.

CONCLUSION

IC individuals had a high COVID-19 disease burden during the Omicron era. Appropriate preventive measures should be continued for this population.