By Yaffa Shir-Raz at Brownstone dot org.

As ACIP deliberated without access to full trial data, an even more alarming pattern was already unfolding in the real world. Now, analysis of the FDA's FAERS database reveals 37 infant deaths out of just 991 reports - a fatality signal nearly twice that of other routine vaccines. Why was this not disclosed?

The warning sign was already visible in the clinical trials: infant deaths in the treatment groups were twice as frequent as in the control arms - a signal that should have triggered immediate scrutiny. As documented in a previous Brownstone article, this alarming imbalance was withheld from ACIP during its June 2025 review of Merck's competing RSV antibody, Clesrovimab.

Now it emerges that this was not the only red flag kept from the committee. An analysis of real-world data from the FDA's adverse event reporting system (FAERS) reveals an even starker reality: since Sanofi's Beyfortus (nirsevimab), which was approved and added to the US infant immunization schedule in 2023, there have been 1,012 adverse event reports - including 37 infant deaths, a concentration rarely seen in pediatric vaccine safety profiles.

A Disproportionate Share of Deaths

As of September 29, 2025, the FAERS database lists 1,012 adverse event reports for Beyfortus, including 684 serious cases and 37 infant deaths (see Figure 1). This reflects a proportion of reported deaths of 3.6% - far higher than historical norms. A comprehensive CDC surveillance study (1991-2001) found that deaths typically comprised only 1.4% to 2.3% of all pediatric VAERS reports.

A 2023 systematic review covering over three decades of VAERS data similarly found that deaths accounted for just 1.0% of all reports across all age groups, with most years staying below 2%, and only isolated spikes in the early 1990s exceeding that level. Against this backdrop, the proportion of reported Beyfortus cases involving infant deaths appears nearly double the historical average.

The overall severity profile is equally concerning. Of the 1,012 total Beyfortus reports in FAERS, 684 (67.4%) were classified as serious adverse events - defined as hospitalization, life-threatening conditions, disability, or death. As detailed above, this includes 37 infant deaths (3.6%). The remaining serious cases include 415 hospitalizations (40.9%) and 46 life-threatening events (4.5%).

For comparison, the same CDC study found that only 14.2% of reports were classified as serious, while the 2023 systematic review reported hospitalization rates of just 5.8% and life-threatening events at 1.4% of all reports. These benchmarks underscore how disproportionately severe the adverse event profile is for Beyfortus.



While VAERS reports do not establish causality, they are widely used by regulators for signal detection. Importantly, even established passive surveillance systems such as VAERS are estimated to capture only 1-10% of actual adverse events. These patterns, even if preliminary, merit urgent investigation, not dismissal.

A Seasonal Mortality Pattern Hidden from Reviewers

At first glance, one might suggest that the rising number of deaths simply reflects the expansion of Beyfortus use. Yet the timeline tells a more nuanced story - one that reveals a growing and disproportionate signal, even before full-scale uptake.

Before examining the seasonal trends in detail, it is important to understand the scale of uptake. During the 2023-2024 RSV season - the first season in which either nirsevimab or the maternal RSV vaccine was available - CDC data show that only 29% of eligible infants were immunized through either route. State-level coverage ranged from just 11% to 53% (CDC, 2024).

This limited adoption is critical context: if serious adverse events are already emerging at submaximal coverage, what will happen as usage expands?

The year-by-year timeline of deaths provides an instructive contrast:

2023: Beyfortus was rolled out only in October, with a limited three-month ...