Paper Information

We updated a model of SARS-CoV-2 infections to align with the latest evidence on SARS-CoV-2 natural history and waning of immunity, and to integrate various data sources available throughout the pandemic. We used this model to produce population estimates of effective protection against SARS-CoV-2 infection and severe COVID-19 disease.

A new wave of SARS-CoV-2 infections and COVID-19-associated hospitalizations began near the end of 2023, with the introduction of the JN.1 variant. This upturn suggests that the U.S. population remains at risk of SARS-CoV-2 infection and severe COVID-19 disease despite the high level of cumulative exposure in the United States. This decline in effective protection is likely due to both waning and continued viral evolution.

On December 30, 2023, 98.6% of the U.S. population had experienced immunological exposure to SARS-CoV-2 through infection and/or vaccination, with 88.3% (95% credible interval (CrI): 78.4%, 95.5%) having had at least one SARS-CoV-2 infection. Despite this high exposure, the average population-level protection against infection was 31.6% (25.1%, 41.2%). Population-level protection against severe disease was 66.1% (59.2%, 74.3%).

Effective immune protection against SARS-CoV-2 infection and severe COVID-19 disease continues to change due to viral evolution and waning immunity. We estimated population-level immunity to SARS-CoV-2 for each of the fifty United States (U.S.) and the District of Columbia from January 2020 through December 2023.