Hossein Estiri, PhD, an assistant investigator in the Laboratory of Computer Science at Massachusetts General Hospital, along with Alaleh Azhir, a medical student at Harvard and MIT, co-authored a research letter in the journal JAMA Network Open, “Severity of COVID-19–Related Illness in Massachusetts, July 2021 to December 2022.”

What Question Were You Investigating?

It is difficult to track the real severity of COVID-19 variants as severity changes over time because our immunity is also changing (getting vaccines or infected) and the healthcare system is also evolving over time.


In this study, we tried to show how the severity of the virus itself has been changing over time. We wanted to know, is the "true" severity of COVID diminishing in Massachusetts?

What Was Your Approach?

We performed a weighted causal inference study and defined severity based on specific outcomes as well as the interaction between the virus, the host (human), and the healthcare system – i.e., given prior infections, vaccination and healthcare system capabilities.

What Were Your Findings?

We show a diminishing severity profile over time that seems to have stabilized during 2022. SARS-CoV-2’s severity waned between July 2021 and September 2022 after adjusting for confounders of vaccination status.

Overall, vaccination is still associated with a decrease in the risk of severe SARS-CoV-2 outcomes. With the variants demonstrating milder severity over recent months, it is reasonable to presume that our findings are broadly generalizable.

What Are the Implications of Your Findings?

Based on this work, we are launching a prediction dashboard online that predicts severity in the next one to three months. The dashboard enables us to quantify and visualize the severity profile across patient sub-groups and the overall population. It can also inform public health officials and the public about how the virus is evolving under immunizations and healthcare capacities.

About the Massachusetts General Hospital

Massachusetts General Hospital, founded in 1811, is the original and largest teaching hospital of Harvard Medical School. The Mass General Research Institute conducts the largest hospital-based research program in the nation, with annual research operations of more than $1 billion and comprises more than 9,500 researchers working across more than 30 institutes, centers and departments. In July 2022, Mass General was named #8 in the U.S. News & World Report list of "America’s Best Hospitals." MGH is a founding member of the Mass General Brigham healthcare system.