A recent meeting of the Advisory Committee on Immunization Practices (ACIP) under the US Centers for Disease Control and Prevention (CDC) took an unexpected turn. Instead of the usual data-driven discussions, the CDC scientists found themselves defending vaccine safety and effectiveness against skeptical queries.

The meeting, held over two days, saw new committee members asking pointed questions about Covid-19 vaccines. They questioned the interpretation of data, the criteria for counting hospitalizations, and the potential biases in the studies. This shift in tone was notable, as the committee typically relies on CDC experts to present and interpret data.

The agenda included presentations on long-standing topics that have fueled vaccine skepticism: the preservative thimerosal and the rare febrile seizures associated with some combination measles vaccines. Notably, these presentations were not given by CDC staff but by a newly appointed committee chair and a former leader of an anti-vaccine organization.

The meeting also highlighted the ongoing debate about Covid-19 vaccines for healthy children and pregnant women. Following a recent announcement by the US Health and Human Services Secretary, the CDC presented data showing high hospitalization rates for very young children. Committee members discussed the interpretation of this data, with some questioning whether the hospitalizations were directly due to Covid-19 or incidental.

The discussion on thimerosal, a preservative used in some vaccines, was particularly contentious. Despite numerous studies showing no link between thimerosal and neurodevelopmental problems, the presentation suggested that thimerosal is ineffective and unsafe. This presentation was troubling to some experts, who feared it could erode trust in vaccination programs.

The meeting also touched on the rare but serious side effects of the combination MMRV vaccine. The CDC's evidence review noted that while febrile seizures can occur, they are rare and resolve without long-term consequences. The committee announced plans to reevaluate the recommendation for this vaccine, which could have implications for vaccination schedules.

Throughout the meeting, there was a clear tension between the CDC scientists and some committee members. The scientists emphasized the rigorous methods used to ensure the accuracy of their data, while the committee members raised concerns about potential biases and confounding factors. This tension underscores the broader challenges faced by public health agencies in maintaining trust and credibility in the face of vaccine skepticism.

Vaccine Debates: New Faces, Old Questions

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