June 18 (UPI) -- A senior scientist at the U.S. Centers for Disease Control and Prevention has resigned, warning that changes in leadership may weaken the country's vaccine program.

Dr. Fiona Havers, who led the CDC's tracking of hospitalizations from COVID-19 and respiratory syncytial virus, stepped down this week.

"Unfortunately," she said in an email to colleagues, " I no longer have confidence that these data will be used objectively or evaluated with appropriate scientific rigor to make evidence-based vaccine policy decisions." The memo was obtained by The Washington Post.

Havers' departure comes just days after U.S. Health and Human Services Secretary Robert F. Kennedy Jr. removed all members of the CDC's Advisory Committee on Immunization Practices and replaced them with new appointees. The panel makes recommendations on use of vaccines in the United States.

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