# Estimating the decay of protective antibodies induced by SARS-CoV-2 mRNA vaccination and hybrid immunity

## TL;DR

This study tracks how long antibodies from SARS-CoV-2 mRNA vaccines last in healthy adults and finds that a booster or hybrid immunity significantly extends protection.

## Contribution

The study provides new insights into antibody decay rates after mRNA vaccination and hybrid immunity in healthy adults.

## Key findings

- Two-dose vaccine antibody levels decay with a half-life of 59.8 days.
- A booster dose increases the half-life to 99.7 days.
- Hybrid immunity extends antibody half-life to 241 days.

## Abstract

Starting in 2020, we quantified anti-wildtype SARS-CoV-2 spike sera IgG at monthly intervals from generally healthy adults after various doses of mRNA-based COVID-19 vaccination and in the context of hybrid immunity. Confirmed post-vaccination infections and subclinical infections identified by longitudinal serology were removed from vaccine-only analyses. Over 400 days, the two-dose vaccine-alone antibody response decayed at a half-life (t1/2) of 59.8 days compared with a t1/2 of 99.7 days after receipt of one booster dose. In the hybrid immunity model, the t1/2 was greater at 241 days. Using cut-offs for correlation of protection obtained in a prior study, we modeled that individuals with hybrid immunity maintain antibody levels above a 75% correlate of immunity for 283 days after an immune-boosting event. These data offer insights into SARS-CoV-2 antibody decay kinetics that may inform COVID-19 vaccine timing in the younger (age under 60), healthy adult population.