They collect data and make recommendations.
The rest of the world is out here waiting for you, please wake up. We need everyone to make this work.
The CDC's mission is fundamentally the same as the mission of the Chinese disease control agency. The difference is how that mission is balanced against people's freedom to live their lives.
Please don't misunderstand; that doesn't mean that I oppose everything they do. Everything they do limits freedom, but sometimes that is necessary.
It's a scientific question as to whether a specific limit on freedom (of movement, of contact, etc.) is effective.
But it's a general approximation that greater freedoms mean higher mortality rates during lethal pandemics. And vice versus.
What level of mortality we're prepared to accept, and what level of limitations on freedom, is a political question in a democracy.
That's the eternal question. Not just for disease control, but for everything.
> What are the criteria for determining necessity?
In a democracy, ultimately: elections.