By Stephanie Stahl

PHILADELPHIA (CBS) — The U.S. Food and Drug Administration is recommending COVID-19 boosters for the Moderna and Johnson & Johnson vaccines and also approved mixing different vaccine brands.

The Moderna booster is recommended for people at high-risk, and it will be half the dose that was in the first two shots. It should be given six months after the second dose. People who received the J&J vaccine should get a second dose two months after their initial vaccination.

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The FDA followed the recommendation of its advisory panel and has cleared booster shots for Moderna and Johnson & Johnson. Authorization from the U.S. Centers for Disease Control and Prevention is needed before they’ll be available.

Officials are hoping boosters become more popular. Pfizer’s, which was approved last month, hasn’t been.

“There are a number of reasons for demand not being higher,” New Jersey Gov. Phil Murphy said. “I think there was some mixed messaging out of the feds and probably some false sense of security.”

In Philadelphia, the acting health commissioner says the city is doing outreach to get more people to get booster shots — a critical move because the virus is still a threat.

“We’re still at high transmission, we still have significant numbers of people in the hospital, but we aren’t seeing a surge of cases,” Dr. Cheryl Bettigole said.

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The FDA has also approved mixing and matching vaccines. For example, a person who received a Johnson & Johnson shot could get Pfizer or Moderna vaccine as a booster.

“In the real world, all of these kinds of combinations or extra boosters are already happening so I think it’s a matter of urgency,” Dr. Ofer Levy with the FDA advisory said.

Research shows mixing vaccines can be beneficial.

“Presenting things to your immune system in two slightly different ways may enhance the ability to boost things, give better quality to that boosted immune response,” Dr. John Wherry with Penn said.

Researchers say boosters are coming at just the right time with cooler temperatures and more people inside, the virus could surge again. They add being protected before the holiday season is important.

“Getting vaccinated and if eligible, receiving a booster, is the number one step you can take for a safe holiday,” New Jersey Health Commissioner Judy Persichilli said.

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Before the newly FDA-recommended booster shots become available, they have to be authorized by the CDC. That group is meeting Thursday.

Stephanie Stahl