CNN  — 

Booster shots are here, after much hoopla from the White House and a great deal of discussion and consideration from the teams of doctors and other experts who advise the US Food and Drug Administration and the US Centers for Disease Control and Prevention.

More than 2 million people have already received third doses of Pfizer’s coronavirus vaccine, but these technically were not booster shots – they were extra doses given to people whose immune systems are compromised and may not have responded fully to the first two doses of vaccines.

But now the CDC and FDA have agreed many Americans need boosters and should start getting them. Here are some important things to know about them:

Who is eligible?

Many adults will be eligible for boosters if they have already received two doses of Pfizer’s vaccine.

“Starting today, if you are six months out from your last dose of the Pfizer vaccine, you are eligible for a booster if you fall into one of three high risk groups,” US Surgeon General Dr. Vivek Murthy told a White House Covid-19 briefing Friday.

“Number one: You are 65 or older. Number two: You have a medical condition that puts you at high risk of severe illness with Covid and these conditions include obesity, diabetes, high blood pressure, chronic kidney disease and others. And Number three: You work or live in a setting where you are at high risk of exposure to Covid. This includes health care workers, teachers, those living in shelters or prisons and grocery store workers.”

The federal government website at has links to pages outlining who is eligible for a booster shot and has lists of locations where shots are available.

The CDC’s Dr. Kathleen Dooling told the Advisory Committee on Immunization Practices earlier this week there is a wide variety of people who might be included in the high risk groups. “Fully vaccinated persons with underlying medical conditions may be at risk of severe COVID-19 if they become infected with SARS-CoV-2,” she said. They include cancer, stroke, chronic kidney disease, chronic obstructive pulmonary disease or COPD, diabetes, heart conditions, obesity, pregnancy and smoking.

White House Covid-19 coordinator Jeff Zients said up to 20 million Americans fall into these categories as of now.

When and where can people get one?

People have already started getting booster shots.

Zients said there is plenty of supply, and people should be able to get boosters at pharmacies, doctors’ offices and sometimes at mass vaccination sites.

“Boosters will be free for everyone, regardless of immigration or health insurance status. No ID or insurance required,” he said Friday.

“And we’ve worked closely with partners including governors, pharmacies, doctors, long term care facilities and other providers so that eligible Americans are able to get a booster shot at roughly 80,000 places across the country, including over 40,000 local pharmacies,” Zients added.