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An estimated 29% of infants born between October 2023 and March 2024 were immunized against RSV, according to a CDC report published in late August. Those numbers appear to be rising, even as new details raise questions about the shot’s safety.
In its latest Morbidity and Mortality Weekly Report, the Centers for Disease Control and Prevention (CDC) said that during the 2023-2024 season — the first season RSV shots for mothers and infants were available — immunization rates varied widely by state, ranging from 10.8% to 53.1%.
Immunization occurred either through maternal vaccination with Pfizer’s Abrysvo (10%) or infant immunization with the monoclonal antibody nirsevimab (19%), marketed as Beyfortus by AstraZeneca and Sanofi. Those were the only shots available at the time.
The CDC authors speculated that the low numbers may have been due to supply issues, lack of familiarity with the shots and cost. Under the Affordable Care Act, there is a one-year grace period for insurers to cover immunizations recommended by the Advisory Committee on Immunization Practices (ACIP).
During the ACIP’s June 25 meeting, CDC researchers presented preliminary data from an internet survey indicating that immunization rates increased to 57% during the 2024-2025 season.
Also at that meeting, the committee recommended Merck’s new RSV monoclonal antibody shot clesrovimab, marketed as Enflonsia.
Sanofi data showed increased risk of seizure, but findings obscured
Investigative journalist Maryanne Demasi, Ph.D., reported Aug. 17 that researchers for the CDC appear to have presented misleading data on Sanofi’s monoclonal antibody shots to ACIP members before their vote on Merck’s RSV shot.
Dr. Matthew Daley, a pediatrician at Kaiser Permanente Colorado — which receives funding from Sanofi — presented the post-marketing data on Sanofi’s RSV shot in the 2023-2024 season.
Daley split the data on seizures into two groups — babies ages 0 to 37 days and babies ages 38 days to under 8 months. The former were 3.5 times more likely to have a seizure after injection, and the latter were 4.38 times more likely.
Neither was statistically significant, leading Daley to conclude the CDC data showed “no significant increased risk.”
However, if the two groups are combined and analyzed using a meta-analysis, babies are nearly four times more likely to have a seizure after receiving the Sanofi RSV injection. Those results are statistically significant, Demasi reported.
Demasi, who said independent analysts verified the findings, wrote:
“By splitting the cases into two groups, the signal of harm effectively vanished. ACIP members were never shown the pooled result.
“The choice to divide the data at 37 days is puzzling.
“There is no clear clinical or biological reason for that cutoff — it looks entirely arbitrary, fueling suspicion it was chosen after the fact, once the results were known.”
Daley didn’t present the full analysis to the ACIP members. Demasi said that may have influenced their decision on Merck’s monoclonal shots because the seizure risk “is likely to be a class effect, meaning it could apply to all RSV monoclonal antibodies now approved.”
Two days after Demasi posted her analysis on Substack, ACIP panel member Dr. Robert Malone said he regretted his vote on Merck’s RSV antibody, as it relied on “manipulated data.”
CDC officials declined to comment on Demasi’s findings. The U.S. Department of Health and Human Services stated that ACIP will continue to closely monitor the antibodies.
In June, ACIP members dismiss concerns over RSV shots
The U.S. Food and Drug Administration (FDA) first approved Merck’s clesrovimab shot on June 9.
On June 10, The Defender reported that the FDA approved Merck’s product even though, according to the government website ClinicalTrials.gov, adverse events — including deaths, respiratory infections, febrile convulsions, seizures, facial paralysis and brain injury — occurred at higher rates among the infants that received the shot.
At the ACIP meeting, committee member Retsef Levi, Ph.D., raised concerns that the babies in the intervention group in the trial showed a higher rate of nervous system-related serious adverse events than babies in the control group, according to Demasi.
Levi also noted that in one trial, there were five deaths in the group of babies who received the monoclonal antibodies and none in the placebo group. In another, when compared with an existing treatment, the death ratio was 5-to-1. In a third trial, it was 7-to-3.
“Should we not be concerned about these potential safety signals?” he asked.
Merck said it had analyzed the data and none of the events were related to the shot. It also noted that the differences were not statistically significant.
Levi also noted that the trials were too small to identify robust safety signals. He said the post-marketing data would be important in understanding the possible dangers of the shots.
Levi and one other committee member, Vicky Pebsworth, Ph.D., opposed recommending the shot. The remaining five members voted to recommend it.
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CDC faced top-level shake-up last week
Demasi’s exposé on the manipulated data was just one of many recent scandals rocking the CDC.
Last week, CDC Director Susan Monarez was ousted and several other senior officials resigned.
One of those officials, Dr. Demetre Daskalakis, was director of the CDC’s National Center for Immunization and Respiratory Disease. In his resignation letter posted on X, he explicitly criticized ACIP members as “people of dubious intent and more dubious scientific rigor” who had been placed in charge of recommending vaccine policy.
Demasi said Daskalakis’ “hypocrisy is striking,” given that his agency was the one responsible for withholding the accurate post-marketing safety data from ACIP members.
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