SARS-CoV-2-associated mortality with a principal cause other than COVID-19 during the Omicron epidemic in France and detection and treatment of Omicron infections in associated complications

Background: With the emergence of the Omicron variant, an increasing proportion of SARS-CoV-2 associated deaths have a principal cause of death other than COVID-19. In France, between Nov. 1, 2021 -- July 31, 2022, in addition to 33,353 deaths with the principal cause of COVID-19, there were 9,638 deaths with a confirmed SARS-CoV-2 infection with a principal cause other than COVID-19 (as well as SARS-CoV-2-associated deaths with an undetected SARS-CoV-2 infection). Methods: We examined the relation between mortality with a principal cause other than COVID-19 (non-COVID-19 mortality) in France during the pandemic and SARS-CoV-2-related ICU admissions in adults aged over 60y. Results: The number of non-COVID-19 deaths in France between July 2021-June 2022 was greater than the corresponding number between July 2020-June 2021 by 20,860 (95% CI (11241,30421)) after adjusting for pre-pandemic trends in mortality. During the period of Omicron circulation, there was a strong temporal association between the weekly rate of non-COVID-19 deaths in France and the rate of ICU admissions with a SARS-CoV-2 infection in adults aged under 60y during the previous week (correlation=0.90 (0.84,0.94)) for the period between Nov. 1, 2021 - Nov. 13. 2022). Proportions of ICU admissions for causes other than COVID-19 among all SARS-CoV-2-positive ICU admissions in older adults were lower during periods of active COVID-19 circulation in France, particularly the first wave of the Omicron epidemic. That pattern persisted for the later period as well, with correlations between the proportion of ICU admissions for causes other than COVID-19 among all SARS-CoV-2 positive ICU admissions and rates of ICU admissions for COVID-19 for the period between March 25, 2022 -- Dec. 5, 2022 ranging from -0.4 (-0.5,-0.3) in ages 70-79y to -0.53 (-0.61,-0.44) in ages over 90y. Conclusions: Our results suggest a significant contribution of Omicron infections to mortality with the principal cause other than COVID-19 in France. Our results also suggest temporal inconsistency in characterizing complications associated with Omicron infections, which may be related to both under-detection of Omicron infections and to temporal differences in the treatment of Omicron infections in associated complications.