What led to AstraZeneca's COVID-19 vaccine being pulled from consideration in the United States?

AstraZeneca's vaccine was removed from the U.S. market after trial participant Brianne Dressen and another person reported identical serious neurological complications to the National Institutes of Health in January 2021. Despite initial promises that the vaccine was safe and effective, these adverse events were not disclosed to participants during the trial phase. The NIH responded within 24 hours to their reports, and within 10 days, two significant actions occurred: AstraZeneca was pulled from consideration in the United States, and the NIH initiated a study to investigate neurological complications following COVID vaccines in general. This demonstrates how individual adverse event reports can directly impact regulatory decisions and public health policy.