The U.S. Centers for Disease Control and Prevention panel on Thursday recommended Pfizer's tweaked COVID-19 booster that targets the newest omicron strains for people 12 and older.
The panel also voted to recommend Moderna’s version of the booster update, to be used in adults only.
The panel’s recommendation comes after the U.S. Food and Drug Administration gave the shot the green light in a fast-tracked approach. CDC’s director Dr. Rochelle Walensky must give the final sign-off before the shots are available.
In June, the FDA ordered vaccine makers to tweak their shots to target BA.4 and BA.5, becoming the so-called "combo shot."
FILE - Medical staff at Howard University give COVID-19 Vaccination doses for Hospital Staff Members on Dec. 15, 2020 in Washington, DC.
Currently, the BA.5 strain is causing nearly all COVID-19 infections in the U.S. and much of the world. Authorities are taking a gamble that the strain, or something similar, will still be the biggest threat in the coming months and, to get ahead of another mutation possibly transpiring, have fast-tracked approval of a targeted booster.
Current COVID-19 vaccines match the strain that circulated in early 2020. And while those vaccinations still offer strong protection against serious illness or death, there’s little effectiveness against infection from the wildly mutated omicron family.
To approve the combo shot, FDA relied heavily on scientific testing of prior vaccine tweaks rather than on a human study of the BA.5-tweak’s effectiveness, which could take months. A wait that long heightens the risk that another mutation could take over.
This means authorities are taking a gamble on how effective the combo shot will be.
How does the combo shot work?
Think of the combination shot as a second-generation vaccine. And if you want to be on par with the scientists, call it a "bivalent" shot.
A bivalent shot strategy allows a shot to keep the proven benefits of the original vaccine while adding to its protection.
It’s a common vaccine strategy: Flu shots, for instance, can protect against four influenza strains and are tweaked annually depending on what’s circulating.
Both the Pfizer and Moderna vaccines contain the genetic instructions for the spike protein that coats the coronavirus, to train the immune system to recognize the real virus. The new combo doses will contain half that original vaccine recipe and half protection against the newest omicron versions, called BA.4 and BA.5.
The U.S. is the only country so far to go for this bivalent shot strategy.
Earlier in August, Britain authorized a different update to Moderna’s shot that adds protection against the original omicron that struck last winter. European regulators also are considering the original omicron versions by Moderna and Pfizer, meaning different countries will be using different versions of booster shots this fall.
How was the combo shot tested?
Instead of risking the months’ wait for data from a human study on BA.5, researchers have relied heavily on other studies.
To evaluate the combo shots, FDA used data from human testing of the earlier BA.1-tweaked doses plus tests on mice of the BA.5-targeted version.
It’s a gamble, as researchers can’t say for sure how effective the tweaked version will be, and many consider the strategy controversial.
"For the FDA to rely on mouse data is just bizarre, in my opinion," John Moore, an immunologist at Weill Cornell Medicine in New York, told NPR. "Mouse data are not going to be predictive in any way of what you would see in humans."
Dr. Peter Marks, the FDA's vaccine chief, told The Associated Press the data from both studies show "a very good immune response."
Human data on the newest tweak will come later in the year, to help assess the value of modified shots — especially whether they offer cross-protection if a new mutant comes along, Marks said.
Moderna has started a clinical trial of its BA.5 combo shot; Pfizer and its partner BioNTech expect to open a similar study soon.
Whether or not Americans will take the updated shot is to be seen as well.
While three-quarters of Americans 12 and older have gotten their initial vaccinations, only half got a first booster shot — deemed crucial for the best protection against variants. And just a third of people 50 and older who were advised to get a second booster when omicron arrived did so.
Prior to the shot’s approval, the Biden administration began stressing its value.
"It’s going to be really important that people this fall and winter get the new shots. It’s designed for the virus that’s out there," White House COVID-19 coordinator Dr. Ashish Jha said.
This story was reported from Detroit. The Associated Press contributed.