No excess mortality during the Delta variant era in US state with high vaccination rates

The coronavirus disease 2019 (COVID-19) pandemic spread rapidly around the globe, and excess mortality was seen worldwide in the initial outbreak. Mass vaccination programs, drug repurposing, and monoclonal antibody treatments have contributed to controlling the disease's spread and severity, but worries remain over the rise of variant strains. Of particular concern is the Delta variant, which is known to escape both natural and vaccine-induced immunity.

Researchers from the Harvard School Of Medicine have taken this opportunity to investigate the number of excess deaths during the initial spread of the Delta variant. A preprint version of the study is available on the medRxiv* server while the article undergoes peer review.

Study: Absence of Excess Mortality in a Highly Vaccinated Population During the Initial Covid-19 Delta Period. Image Credit: Lazy_Bear/ ShutterstockStudy: Absence of Excess Mortality in a Highly Vaccinated Population During the Initial Covid-19 Delta Period. Image Credit: Lazy_Bear/ Shutterstock

The study

The researchers examined data from the Massachusetts Department of Health, including total deaths, COVID-19 attributed deaths, and weekly coronavirus cases. They used five years of previous data from the US Census and statistics from the Centers For Disease Control in their seasonal autoregressive integrated moving average (sARIMA) model to determine expected and excess deaths within given periods. These models are the traditional choice for handling data with a trend over time. Unlike the regular variant, sARIMAs can also forecast data with a trend that can be affected by seasonal changes in data.

From there, the scientists examined excess deaths compared to COVID-19 deaths during the first wave, second wave, and then during the spread of the Delta variant. They also took into account vaccination, both state-wide and in individual counties.

Between March and June 2020, when COVID-19 originally spread to the US, there were over 100,000 cases, 7878 attributed deaths, and 7775 excess deaths. Excess deaths are the number of fatalities exceeding the previously expected number. More excess deaths were recorded in early March than Covid-19 attributed deaths- possibly due to a lack of testing.

However, COVID-19 attributed deaths have remained above excess deaths since this point, which suggests that some deaths were misattributed to the disease. This could be through misdiagnosis or merely as COVID-19 contributed to the death rather than the primary cause.

Between July and September 2020, COVID-19 cases fell to just over 25,000, with 1334 COVID-19 attributed deaths. Deaths in total were lower than expected, which the researchers theorize is due to deaths that would have occurred in this time being 'pulled forward' by the pandemic.

Between October 2020 and March 2021, the second wave of COVID-19 hit the USA, and cases rose dramatically to 466,100. Deaths caused by COVID-19 also rose, reaching 7603, while excess deaths were once again lower, at 3282. This pattern continues throughout the spring of 2021.

The Delta variants arrived in large (above 10% of cases) numbers in Massachusetts in June 2021. While cases hit just under 58,000, widespread vaccination proved effective, and only 342 deaths were attributed to the disease.

Once again, not only were no excess deaths reported, but fewer deaths occurred than expected. This was not the case in 2 counties, which saw a rise of over 10% of excess deaths. These were the least two vaccinated counties in Massachusetts.

Figure. Weekly all-cause excess deaths in Massachusetts (blue line) and Covid-19-attributed deaths (orange line) in Massachusetts. The baseline (gray line) was determined using sARIMA and reflects five years of population growth, weekly mortality data, and population changes owing to the total cumulative excess deaths recorded during the pandemic.Figure. Weekly all-cause excess deaths in Massachusetts (blue line) and Covid-19-attributed deaths (orange line) in Massachusetts. The baseline (gray line) was determined using sARIMA and reflects five years of population growth, weekly mortality data, and population changes owing to the total cumulative excess deaths recorded during the pandemic.

Conclusion

The authors determine their findings indicate that vaccination remains effective in preventing the more severe forms of the disease, as well as lowering deaths attributed to COVID-19, even against alternate variants of the disease. This comes as welcome news as other studies have begun to record lower immune responses and anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) activity among antibodies gained through immunity to the strain of the disease originally seen in Wuhan, China, is lower against the Delta variant.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established

Journal reference:
Sam Hancock

Written by

Sam Hancock

Sam completed his MSci in Genetics at the University of Nottingham in 2019, fuelled initially by an interest in genetic ageing. As part of his degree, he also investigated the role of rnh genes in originless replication in archaea.

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