Excess mortality rates from chronic illnesses and other natural causes were driven by COVID-19 infections, according to a new study.

While excess mortality provides an estimation of deaths that likely would not have occurred under normal, non-pandemic conditions, there is still little evidence into whether the SARS-CoV-2 virus contributed to the additional deaths, or whether these deaths were caused by other factors such as healthcare disruptions or socioeconomic challenges or COVID vaccinations.

The new study led by the Boston University School of Public Health (BUSPH) and the University of Pennsylvania (UPenn) provides the first concrete data showing that many of these excess deaths were indeed uncounted COVID deaths.

Published in the journal PNAS, the study compared reported COVID-19 deaths to excess deaths due to non-COVID natural causes, such as diseases and chronic illnesses.

They found that increases in non-COVID excess deaths occurred at the same time or in the month before increases in reported Covid deaths in most US counties.

Focusing on excess deaths by natural causes rather than all-cause excess death estimates provides a more accurate understanding of the true number of deaths attributable to COVID-19, as it eliminates external causes for mortality, such as intentional or unintentional injuries, for which COVID would not be a contributing factor.

"Our findings show that many COVID-19 deaths went uncounted during the pandemic. Surprisingly, these undercounts persisted well beyond the initial phase of the pandemic," said Dr. Andrew Stokes, Associate Professor of global health at BUSPH.

The temporal correlation between reported COVID deaths and excess deaths reported to non-COVID natural causes offers insight into the causes of these deaths, he said.

"We observed peaks in non-COVID-19 excess deaths in the same or prior month as COVID-19 deaths, a pattern consistent with these being unrecognised COVID-19 deaths that were missed due to low community awareness and a lack of COVID-19 testing."

If the primary explanation for these deaths were health care interruptions and delays in care, the non-COVID excess deaths would likely occur after a peak in reported COVID-19 deaths and subsequent interruptions in care, said lead author Eugenio Paglino, a doctoral student studying demography and sociology at UPenn.

"However, this pattern was not observed nationally or in any of the geographic subregions we assessed," Paglino said.