Since mid-September, Covid-19 booster shots have been available to anyone age 18 and older in the United States. But who needs one the most? And how long do initial vaccines last before you need a booster? Medical professionals offer some insight.

How long do you have to wait after your initial shot to get a booster?

Those who received Moderna or Pfizer BioNTech vaccines originally should wait six months before getting a booster.

The CDC now advises  anyone 18 and older who got the single-dose Johnson & Johnson vaccine to get a second dose two months after the initial shot. This can amp up your protection.

Can you mix and match shots?

According to the CDC, a booster shot does not have to match the brand of the first vaccine you had. For instance, if you received Moderna first, you can get a Pfizer booster and vice versa. Your choice could depend on the side effects you had from the initial dose, convenience and what's available in your area.

Who needs the booster most?

People who are age 65 and older, people ages 50 to 64 with underlying health conditions, people in high-risk settings like healthcare, and adults 18 or older who live in long-term care settings should all get booster shots six months after their initial vaccine series. These populations are all at higher risk of contracting Covid-19 and experiencing complications.

What if you are not immunocompromised?

Aside from those who are immunocompromised or who only received one dose of Johnson & Johnson vaccine, infectious disease epidemiologist Dr. David Dowdy, of Johns Hopkins Bloomberg School of Public Health, told NPR it's a "closer call" about who needs to get the booster right away. "For the vast majority of people, there’s not an immediate urgency to run out and get this booster,” says Dowdy. (That doesn't mean you shouldn't plan on getting one, though.)

Does the initial vaccine lose effectiveness over time?

"Over time, the vaccine's protection is reduced because the antibodies your body made to fight this virus start decreasing," Sarasota Memorial infectious disease specialist Dr. Manuel Gordillo said in a video for the hospital.

"When they were first rolled out, the mRNA vaccines from Pfizer and Moderna offered about 94 percent protection," Gordillo explained. "But now with the Delta variant and the decrease in antibodies from vaccines given eight or nine months ago, we are down to about 80 percent protection. Boosters may be necessary for adequate protection now."

Where can you get booster shots in Sarasota-Manatee?

Pharmacies including Publix, Walgreens and CVS offer booster shots. Department of Health vaccination sites will also offer boosters.