SARS-CoV-2 antibody levels predict COVID vaccine efficacy, study finds

COVID-19 Scan for Nov 24, 2021 CIDRAP

SARS-CoV-2 antibody concentrations predict COVID-19 vaccine effectiveness, with higher levels correlating with greater protection, according to an ongoing US phase 3 clinical trial yesterday in Science.

A team led by researchers from Fred Hutchinson Cancer Research Center in Seattle evaluated 30,420 adult recipients of the Moderna mRNA COVID-19 vaccine at 99 centers for neutralizing and binding antibodies as correlates of risk for, and protection against, infection.

They measured the antibodies at the second vaccine dose and then again 4 weeks later. Concentrations were inversely associated with COVID-19 infection risk and directly tied to vaccine efficacy.

Vaccine effectiveness in vaccinees with 50% neutralizing antibody levels of 10, 100, and 1,000 international units per milliliter was 78% (95% confidence interval [CI], 54 to 89%), 91% (95% CI, 87% to 94%), and 96% (95% CI, 94% to 98%), respectively.

Based on antibody levels, the estimated risk of SARS-CoV-2 infection was roughly 10 times lower for vaccinees whose antibody concentrations were in the top 10% of values, relative to those with negative or undetectable values.

The results help define immune marker correlates of protection, or biomarkers to measure how much immunity is needed to prevent COVID-19 infection, the study authors said. Identifying and validating a correlate of protection would expedite vaccine research and regulatory approval for existing vaccines for new groups of people, modifications of vaccine regimens, and new vaccines, they added. ...