INTRODUCTION
In the United States, infection with SARS-CoV-2 caused 380,000 reported
deaths from March to December 2020.1 Reported deaths
likely underestimate the true number of COVID-19 deaths for a variety of
reasons.2 To better reflect the mortality burden of
the COVID-19 pandemic, various estimates of excess deaths have been
made, where excess deaths are defined as the difference between the
observed numbers of deaths in a specific time period and expected
numbers of deaths in the same time period based on mortality during
prior years. These analyses of all-cause mortality data found large
relative increases in mortality during the pandemic among all age
groups,3 but particularly people 25 to 44 years of
age.4
In the United States and other temperate countries, overall mortality
rates are generally highest during the winter months, with peak weekly
mortality rates usually coinciding temporally with influenza virus
activity.5 Vega and colleagues developed the Moving
Epidemic Method (MEM), a useful analytical tool to compare the severity
of influenza seasons over time, across countries, and across age groups
that may have different baseline levels of morbidity.6The method sets standardized intensity thresholds based on the highest
values of a surveillance indicator observed within recent, prior
seasons. In this way, even though particular age groups or geographic
areas have different baseline levels of mortality, the interpretations
of the thresholds would be similar.
We adapted the MEM to all-cause mortality data from the United States to
assess the severity of the COVID-19 pandemic across age groups and
states. Because case ascertainment, definitions, testing practices, care
seeking behavior, and clinical behavior have all changed in response to
the pandemic,7-9 many of the available data sources
with historical data for estimating severity, such as syndromic
surveillance,6 are complicated by such
pandemic-influenced changes. Additionally, as SARS-COV-2 is novel,
historical cause-specific data are not available for comparison as they
would be for influenza. Recent reports have documented that COVID-19 was
the third leading cause of death in 2020, accounting for more than two
thirds of the increase in all-cause mortality.4,10-12Overall death recording is unlikely to be affected by factors that have
changed during the pandemic (e.g., changes in testing, case
ascertainment, or care seeking behavior); these data may provide
valuable information about the severity of the ongoing COVID-19
pandemic. The purpose of this study was to set intensity thresholds in
all-cause death data from past years with the MEM and use those
thresholds to describe the severity of the COVID-19 pandemic in the
United States over time and by age and by geography.