The guidelines for who’s eligible for the Moderna booster shot against COVID-19 are now much simpler. If you’re an adult 18 years of age and older, you can get a booster six months after you receive your second Moderna vaccine shot.

The blanket permission from the US Centers for Disease Control and Prevention for a third dose of any approved vaccine — not just Moderna — came Friday, after the US Food and Drug Administration’s approval the same day. Multiple states had already authorized booster shots for all adults, without waiting for federal approval. We’ll walk you through the details of receiving a booster dose of the Moderna vaccine. We’ll also explain mixing and matching vaccines from the different drug-makers.

Authorization for the Moderna, Pfizer and Johnson & Johnson booster shots — along with Pfizer vaccines for kids — comes at a time when the deadly and contagious delta variant keeps its hold on the US, causing hospitals in some states to buckle. Epidemiologists worry about another wave of COVID-19 infections as cold weather drives people indoors and as the annual flu season kicks in, socking immune systems.

The FDA-approved COVID-19 vaccines have proved to be highly effective in preventing hospitalization, and those who are unvaccinated are 10 times more likely to be hospitalized if infected. With the federal vaccine mandates, the Biden administration aims to counter the surge and put pressure on anyone who hasn’t been vaccinated. Antiviral drugs could also help.

For more on COVID-19, here’s the latest on COVID-19 vaccines for kids, what to do if you lost your vaccination card, the difference between a booster and a third dose, and what to know about breakthrough infections.

All adults are now eligible for the Moderna booster dose

As of Nov. 19, all adults — those age 18 and older — are eligible to get a booster shot of the COVID-19 vaccine. They qualify if it’s been at least six months since they’ve received their second dose of either the Moderna or Pfizer vaccine. Those who received the Johnson & Johnson vaccine are eligible for a booster dose after two months. Adults are encouraged to get whatever booster dose is available to them, even if that means mixing and matching vaccine boosters (more below).

Yes, it’s safe to mix and match vaccine boosters

The FDA has authorized mixing COVID-19 boosters, which in the US means Moderna, Pfizer and Johnson & Johnson. Anyone eligible for a booster can get any of the available brands of coronavirus vaccines. If you initially received Johnson & Johnson and it’s been two months or longer since you received the initial dose, you’ll be able to get the Moderna or Pfizer booster. If you received Moderna or Pfizer for your first two shots, you could pick any authorized vaccine — including J&J — if you qualify and it’s been six months or longer since your second shot.

What does the Moderna booster shot do?

A COVID-19 booster shot — whether from Moderna, Pfizer or Johnson & Johnson — tops off your immune response and guards against a breakthrough COVID-19 infection as the vaccine’s effectiveness decreases over time.

Recent studies of the Pfizer and AstraZeneca vaccines show that their effectiveness can begin to wane after six months. Moderna said early data suggests that those who received the Moderna vaccine in 2020 are showing a higher rate of breakthrough COVID infections than those vaccinated this year, suggesting the need for a booster to maintain high levels of protection.

Is the Moderna vaccine booster the same as the original two COVID-19 doses?

Yes, almost. As with Pfizer’s booster, the third Moderna shot will be the same vaccine as the first two doses, except it’ll be a half dose. To make your life simpler, Moderna is also working on a combination shot that includes this year’s flu vaccine and its COVID-19 booster vaccine, but that is not available right now.

Where can I get the Moderna booster shot?

According to the White House, boosters will be available at roughly 80,000 places across the country, including over 40,000 local pharmacies. Some 90% of Americans have a vaccine site within 5 miles of where they live. You can check Vaccines.gov to see which vaccines are available where, or call 800-232-0233 for vaccine information.

Is the Moderna COVID-19 booster shot free, or do I have to pay?

All booster shots will be free, regardless of immigration or health insurance status. However, depending on where you get your booster shot — for example, at a local pharmacy — you may be asked to log your insurance status. You may be asked to provide your insurance card information, including your name, date of birth and membership number. You will not be charged for your COVID-19 vaccine or booster shot.

Will I need a fourth COVID booster shot?

The CDC updated its guidance to say that next year, some immunocompromised people will be able to get a fourth COVID-19 booster shot. It’s unclear if other groups will need to get a fourth dose at this time.

For more on coronavirus treatments and vaccines, here’s what we know about monoclonal antibody treatments, the new federal vaccine mandates and why some people may not want the shot.

CNET’s Jessica Rendall contributed to this article.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.