Excess Mortality in the United States During the First Three Months of the COVID-19 Pandemic

Deaths are frequently under-estimated during emergencies, times when accurate mortality estimates are crucial for emergency response. This study estimates excess all-cause, pneumonia, and influenza mortality during the COVID-19 pandemic using the September 11, 2020 release of weekly mortality data from the United States (U.S.) Mortality Surveillance System (MSS) from September 27, 2015 to May 9, 2020, using semiparametric and conventional time-series models in 13 states with high reported COVID-19 deaths and apparently complete mortality data: California, Colorado, Connecticut, Florida, Illinois, Indiana, Louisiana, Massachusetts, Michigan, New Jersey, New York, Pennsylvania, and Washington. We estimated greater excess mortality than official COVID-19 mortality in the U.S. (excess mortality 95% confidence interval (CI) (100013, 127501) vs. 78834 COVID-19 deaths) and 9 states: California (excess mortality 95% CI (3338, 6344) vs. 2849 COVID-19 deaths); Connecticut (excess mortality 95% CI (3095, 3952) vs. 2932 COVID-19 deaths); Illinois (95% CI (4646, 6111) vs. 3525 COVID-19 deaths); Louisiana (excess mortality 95% CI (2341, 3183) vs. 2267 COVID-19 deaths); Massachusetts (95% CI (5562, 7201) vs. 5050 COVID-19 deaths); New Jersey (95% CI (13170, 16058) vs. 10465 COVID-19 deaths); New York (95% CI (32538, 39960) vs. 26584 COVID-19 deaths); and Pennsylvania (95% CI (5125, 6560) vs. 3793 COVID-19 deaths). Conventional model results were consistent with semiparametric results but less precise. Significant excess pneumonia deaths were also found for all locations and we estimated hundreds of excess influenza deaths in New York.

We find that official COVID-19 mortality substantially understates actual mortality, excess deaths cannot be explained entirely by official COVID-19 death counts. Mortality reporting lags appeared to worsen during the pandemic, when timeliness in surveillance systems was most crucial for improving pandemic response.