US experienced higher COVID-19 mortality during delta and omicron waves

By Dr. Sanchari Sinha Dutta, Ph.D.Reviewed by Aimee MolineuxNov 22 2022

A recent study published in JAMA provides the estimates of coronavirus disease 2019 (COVID-19)-related mortality and excess all-cause mortality in the US and 20 peer countries during the delta and omicron waves of infection.

Background

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused significant damage to the global healthcare and economic sectors. The highest number of COVID-19 mortality has been observed in the USA. The country has also experienced higher excess all-cause mortality than others during the year 2020.

With the rapid deployment of effective COVID-19 vaccines, a considerable drop in new cases and mortality has been observed worldwide. However, with the emergence of novel viral variants, a gradual drop in vaccine efficacy has been noticed over time.

In the current study, scientists have compared COVID-19-related mortality and excess all-cause mortality in the US and 20 peer Organization for Economic Co-operation and Development (OECD) countries during the delta and winter omicron waves.  

Study design

The scientists collected the US COVID-19-related mortality, all-cause mortality, and vaccination data from the US Centers for Disease Control and Prevention (CDC). The overall US data and the ten most- and least-vaccinated state data were considered in the analysis.

For other peer countries, they collected COVID-19 mortality data from the World Health Organization (WHO), all-cause mortality data from the OECD databases, and vaccination data from Our World in Data.     

The mortality rates were estimated over two periods: the delta-dominated period (June 2021 to December 2021) and the omicron-dominated period (December 2021 to March 2022). The mortality in each period was compared with the mortality in 2015-2019 to estimate excess all-cause mortality.

Observations

The estimated COVID-19-related mortality rates in the US were 61 per 100,000 and 51 per 100,000 during the delta and omicron periods, respectively. The overall US mortality rate and the state-wise mortality rate according to the vaccination status were significantly higher than that observed in other peer countries.

A significant difference in mortality rate was observed between the states with high and low vaccine coverage. Specifically, states with high vaccine coverage (73%) had 75 deaths per 100,000 persons; in contrast, states with low vaccine coverage (52%) had 146 deaths per 100,000 persons.

The excess all-cause mortality rate in the US was estimated to be 145 per 100,000 persons, which was significantly higher than that observed in other peer countries. However, the excess all-cause mortality rate in states with high vaccine coverage was comparable to that in other peer countries during the combined delta and omicron period.

Considering each period separately, a significantly higher excess all-cause mortality was observed in these states compared to that in many peer countries during the omicron period. However, a considerably lower excess all-cause mortality than COVID-19 mortality was observed in these states during this wave.

Predicted mortality rates

According to the predictions made by matching the US COVID-19 mortality with that of the ten most-vaccinated states, the country would have prevented 122,304 deaths during the combined delta and omicron period.

Similarly, in a condition of identical excess all-cause mortality between the US and the ten most-vaccinated states, the US would have prevented 266,700 deaths during the entire period.

In a condition of identical mortality rates between the US and other peer countries, the US would have prevented 154,622 – 357,899 deaths for COVID-19 and 209,924 – 465,747 for all-cause mortality.  

Study significance

The study estimates that the US experienced significantly higher COVID-19 mortality and excess all-cause mortality than other peer countries during 2021 and early 2022. However, the states with high vaccine coverage do not reflect a similar situation. This finding highlights the importance of COVID-19 vaccination in reducing the mortality rate.