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A recent study led by Yale researchers indicated that the impact of COVID-19 is mitigated by high vaccination rates, suggesting that the disease’s effect on the overall mortality of vaccinated individuals is diminishing. 

The study was conducted using Massachusetts, a state with a relatively high vaccination rate, as an example. Harlan Krumholz, director of the YNHH Center for Outcomes Research and Evaluation, or CORE, was the study’s senior author. Krumholz noted that the measurement of excess mortality, which was refined by CORE and adopted by the CDC, is essential for understanding the progression and overall impact of the pandemic across the country. The study defines excess mortality as “the number of all-cause deaths exceeding the baseline number of expected deaths,” and found that Massachusetts experienced less excess mortality due to COVID-19.

“There is a need for continued surveillance as new variants and waning immunity could change the consequences associated with the virus,” Krumholz said.

The reality of the pandemic is steadily shifting as novel variants along with COVID-19 mitigation efforts, prior infections, immunizations, boosters and available treatments have reduced the current number of fatalities due to the disease.

Krumholz believes that Connecticut’s and other northeastern states’ efforts to immunize their populations have been a driving factor in reducing excess deaths. Even though the findings of the study are encouraging for mortality statistics, Krumholz, who is working with professor Akiko Iwasaki on several Long COVID-19 projects, expressed the need to study the long-term consequences of the pandemic. He also spoke to the importance of studying areas with lower vaccination rates to test the effects of those policies on health. 

Benjamin Renton, a research assistant at Ariadne Labs, who collaborated closely with Jeremy Faust, an instructor at Harvard Medical School and the other senior author of the study, emphasized the collaborative nature of this investigation. 

“Everyone had a different role in the research, from the conception of the study to the wrangling of early data, data analysis and visualization and data interpretation,” Renton said. 

According to Renton, the completion of a study of this scope required extensive collaboration with the CDC, evaluation of other states and the surmounting of numerous obstacles that could compromise the validity of these research findings. He emphasized that rigorous scientific research provides an unbiased assessment as to how the pandemic is affecting deaths in the United States and how vaccines and boosters provide protection against the virus’s most severe outcomes.

The research required extensive data and population information utilization. Researchers used population data from 2014 to 2019 and weekly mortality data from Jan. 2015 to Feb. 2020 to create an applied seasonal autoregressive model to forecast death rates for the month of Feb. 3, 2020 to Jun. 26, 2022. This type of statistical model employs time series data, in this case mortality prior to the pandemic, to better comprehend the data set or predict future trends. In doing so, the statisticians were able to compare the past measures of excess mortality in Massachusetts to the periods during which new waves of COVID-19 occurred throughout the overall pandemic period. 

Due to the complex nature of the work, Chengdan Du, a statistician in CORE who was also involved with the project, said that he ran into various statistical issues and hurdles during the research as he had a seismic role in data analysis. Du expressed his pleasure in working on this project with a “very great team.” He worked alongside Shu-Xia Li, associate director of data management and analytics at CORE, to contribute statistical analysis to the research findings. 

“Dr. Faust provided the data for the data collection from the Massachusetts Registry of Vital Records and Statistics, or MRVRS,” Li said. “He was determined and had a lot of connections to gain access to this data.”

Eighty-one percent of Massachusetts residents have been vaccinated.

Abel Geleta covers Yale New Haven Health (YNHH) for the Science and Technology desk at the News. Previously, he covered stories and topics at the intersection of Science and Social Justice. Originally from Ethiopia, Abel has lived in northern Virginia for the past 12 years. He is currently a junior in Berkeley college studying History of Science, Medicine and Public Health as a scholar in the Global Health Studies Program