New Omicron-targeting COVID-19 boosters are approved. Here's what you need to know.

The Centers for Disease Control and Prevention approved new COVID-19 boosters by Pfizer and Moderna on Thursday, following authorization by the Food and Drug Administration on Wednesday. The new vaccines should start to arrive at clinics within days. Here's what you need to know before getting boosted.

How is this booster different from other COVID-19 vaccines?

The new booster is what’s known as a bivalent vaccine, meaning it offers protection from more than one virus or subtype of a virus. So far the available boosters and primary vaccines have been monovalent, targeting the original strain of SARS-CoV-2. But Pfizer's and Moderna’s new bivalent boosters target both the original strain and the BA.4 and BA.5 Omicron subvariants, which the FDA says are responsible for most cases in the U.S. and are expected to circulate this fall and winter.

The bivalent boosters will replace the monovalent boosters that have been used in the U.S., but Pfizer's and Moderna’s monovalent formulations will continue to be used as primary vaccines.

While this is the first time a bivalent vaccine has been used in the U.S. to fight COVID-19, the employment of bivalent vaccines is nothing new. Dr. Wafaa El-Sadr, a professor of epidemiology and medicine at Columbia University, told Yahoo News that the polio vaccine, for example, was developed to protect against multiple subtypes of the poliovirus, and that this technique “is a good way of keeping up with the coronavirus as it evolves over time.”

Who can get the booster dose?

The Pfizer booster is approved in children and adults ages 12 and older, and the Moderna booster is approved in adults ages 18 and older.

Some have argued that a fall vaccination campaign should focus on reaching the most vulnerable populations, including older and immunocompromised Americans. But during a press conference on Wednesday, the FDA pointed to risks associated with "long COVID" as one reason the new boosters should be available more broadly, saying that a third dose of vaccine can probably reduce the chance of getting long COVID by more than half.

Younger children may be eligible to start receiving the new booster “in the coming weeks,” according to a statement by the CDC, though primary vaccination rates among this group remain low. As of Aug. 24, 37% of children ages 5 to 11 had received one dose of a COVID-19 vaccine, and only 7% of children ages 6 months to 4 years had received a dose, according to the CDC.

When should you get vaccinated?

Individuals will need to wait at least two months after receiving their primary vaccination or at least two months after their most recent booster dose before they can get the new bivalent booster.

In a statement on Thursday, CDC Director Rochelle Walensky said, “If you are eligible, there is no bad time to get your COVID-19 booster.”

El-Sadr advised Americans to get ahead of a possible spike in cases as temperatures drop and people begin congregating indoors.

“I think it’s also important to keep in mind that the time to get a booster is not in the middle of the surge,” El-Sadr said. “We recommend that people take the next booster dose before the anticipated surge, meaning taking these booster doses early in the fall before we encounter a potential surge of COVID-19 this winter.”

What does the data say?

U.S. regulators have said that they are confident in the data supporting the authorization of both Pfizer's and Moderna’s bivalent boosters.

“We have worked closely with the vaccine manufacturers to ensure the development of these updated boosters was done safely and efficiently,” said Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, in a statement released on Wednesday by the agency.

The FDA said the decision to grant emergency-use authorization for the Omicron boosters at this time was based on “the totality of available evidence,” including the extensive safety and effectiveness data of the current mRNA-based COVID-19 vaccines, which have now been administered to billions of people worldwide.

The agency also evaluated data from human studies of bivalent booster vaccines developed by Pfizer and Moderna targeting Omicron BA.1, an earlier version of the virus that is no longer circulating in the U.S. These formulations, however, are “similar to each of the vaccines being authorized,” the FDA said, and give the agency confidence that the approved shots will also be as safe and effective.

In these studies, both Pfizer's and Moderna’s bivalent vaccines targeting Omicron BA.1 were found to generate a significant amount of antibodies in humans compared with the companies’ current booster shots, which target only the ancestral strain of the coronavirus. The BA.1 booster shots were recently approved for use in the U.K.

A concern that has been raised about the authorization of these boosters aimed at Omicron subvariants BA.4 and BA.5 is that there are currently no human studies available showing their effectiveness. Instead, the FDA assessed the shots using data from research on mice.

El-Sadr said this approach is not unusual and pointed out that we rely on mice data to update the annual influenza vaccine.

“Every year, essentially, we conduct the studies and look for the immune response for the vaccine within animals,” El-Sadr said of the flu vaccine. “So it’s not unheard of, and it’s actually been the norm, that as you build over time new types of vaccines, you are measuring their effectiveness by comparing the amount of antibodies that are produced in various animal models,” she added.

Dr. Monica Gandhi, an infectious disease doctor and professor of medicine at the University of California, San Francisco, recognized the importance of the animal data and said she was looking forward to these shots becoming available. However, she said that since this is the first time the mRNA-based COVID-19 vaccines have been updated, she would have liked to see some human data before the shots were made available to the public.

“Being the first time, I think it would be really helpful for the public health trust to have a little more human data,” Gandhi said. “It may not need to be, you know, a full-scale trial and a big trial, but really just even showing [that] antibody responses increase in humans; even that, I think would give the public more trust that we've done a little more vetting of this updated vaccine,” she added.

Both Pfizer and Moderna plan to run human trials for their bivalent boosters. Those studies are expected to start this month, and results should be available later this year, the companies have said.

Will people take it?

Vaccination rates in the U.S. have been lagging behind other developed countries. Only 33% of the U.S. population is currently boosted and two-thirds are fully vaccinated. So now that this new booster is available, will people take it?

During Wednesday’s press conference, FDA Commissioner Robert Califf tried to spur confidence in the bivalent booster by using himself as an example.

“I’ll also tell you I’m turning 71 next month, [and] I will be at the front of the line at the pharmacy getting my vaccination. I’m very confident about this,” Califf said.

With breakthrough cases common even among fully vaccinated and boosted Americans, Marks said the FDA is hoping this new vaccine will not only guard against hospitalization and death, but also offer protection from symptomatic disease the way the first crop of vaccines did in late 2020 and early 2021.

“We don’t know for a fact yet whether we will get to that same level, but that is the goal,” Marks said. “The hope here is not to have to give lots of vaccines each year. It’s hopefully to have this be the vaccine that hopefully holds us for as much of this or for the entire season, if it can,” he added.

El-Sadr emphasized that even if breakthrough cases continue to occur, people should still seek vaccinations because they offer protection from some of the worst outcomes of COVID-19.

“I think the most important thing to keep in mind is that these booster doses save lives,” she said. “I appreciate the disappointment that people have had in terms of getting infected even though they’ve done everything right. But nonetheless, let’s keep in mind what’s most important. These vaccines can keep us out of the hospital and keep us well.”