September 7, 2021

CDC: More than 83% of Americans had COVID-19 antibodies before Delta surge

By: Judy Mathias

Editor's Note

A new study from the Centers for Disease Control and Prevention (CDC) finds that more than 83% of Americans had COVID-19 antibodies before the surge of the Delta variant began.

Researchers examined data from 1,443,519 blood donation specimens obtained before the Delta variant.

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Overall infection-induced COVID-19 antibodies increased from 3.5% in July 2020 to 20.2% in May 2021. Combined infection- and vaccination-induced antibodies were 83.3% in May 2021.

The data indicate that the number of COVID-19 cases reported are fewer than the number of COVID-19 infections that have occurred (at a rate of 2.1 infections per reported case), likely because mildly symptomatic and asymptomatic individuals did not seek testing or medical care, the researchers note.

The CDC now estimates that the Delta variant is causing more than 99% of recent COVID-19 cases in the US (


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