The uncoupling of all-cause excess mortality from Covid-19 cases and associated hospitalizations in late winter and spring of 2022 in a highly vaccinated state. (preprint)

ABSTRACT

Introduction: Since March 2020, all-cause excess mortality (the number of all-cause deaths exceeding the baseline number of expected deaths) has been observed in waves coinciding with Covid-19 outbreaks in the United States. We recently described high levels of excess mortality in Massachusetts during the initial 8-week Omicron wave. However, whether excess mortality continued after that period (during which an outbreak of Omicron subvariants occurred) is unknown. Methods: We applied seasonal autoregressive integrated moving averages to five years of pre-pandemic data provided by the Massachusetts Registry of Vital Records and Statistics (MRVRS) to project the weekly populations and expected deaths for the pandemic period. Observed deaths during the pandemic were also provided by MRVRS and are >99% complete for all study weeks. Results: During the 18-week Omicron subvariant period (the week ending February 27, 2022, through June 26, 2022) the incidence of all-cause excess mortality was 0.1 per 100,000-person weeks, corresponding to 148 excess deaths (95%. CI -907 to 1153), representing a 97.1% decrease from the initial Omicron period (during which all-cause excess mortality was 4.0 per 100,000-person-weeks), and a 91.9% reduction from the Delta and Delta-Omicron transition period (during which all-cause excess mortality was 1.5 per 100,000-person-weeks), despite >226,000 reported new Covid-19 cases during the subvariant/spring period. However, Covid-19-associated hospitalizations were observed during the subvariant/spring 2022 period. Conclusion: In a highly vaccinated state with a recent wave of SARS-CoV-2, all-cause excess mortality was uncoupled from new case counts, indicating the possibility of temporary protection from the most severe outcomes related to Covid-19 among high-risk individuals. However, given the possibility of waning immunity and the emerging of new variants, continued monitoring is warranted.