The healthcare clash comes following a wave of COVID cases and as the annual flu season nears. For decades, the CDC has been the nation’s trusted authority on vaccines — setting childhood immunization schedules, guiding which shots adults should receive and shaping state health policies across the country.

Four Western states are taking a different approach from the U.S. Centers for Disease Control and Prevention (CDC) on vaccines for COVID-19, flu and RSV.

Over the last few weeks, people in some states have reported frustration in getting access to the shots, as pharmacies awaited official guidance from the CDC’s advisory committee.