Moderna’s mRNA vaccine against RSV takes a tumble

The latest trial data demonstrates the dangerous speed of innovation.

In September 2024, Moderna announced that the clinical trial of its mRNA vaccine for respiratory syncytial virus (RSV) in children aged 5–24 months was abruptly halted.

The clinical trial, conducted in the UK and other countries, ended after alarming data suggested that the vaccine might not just fail to prevent severe RSV disease, but could potentially worsen it.

Until now, the data were kept secret.

This week, the Food and Drug Administration (FDA) disclosed that vaccinated children in the trial experienced higher rates of severe RSV compared to those in the placebo group.

The data were striking: