The Omicron Booster: Your Questions Answered > News – Yale Medicine

BY CARRIE MACMILLAN December 20, 2022
[Originally published: Sept. 23, 2022. Updated: Dec. 20, 2022.]
When the mRNA COVID-19 vaccines were first unveiled in December 2020, medical experts touted the benefits of this new technology, saying formulations could easily be tweaked someday to match a quickly changing virus. That day has finally come.
In the fall of 2022, the Food and Drug Administration (FDA) authorized—and the Centers for Disease Control and Prevention (CDC) recommended—two updated boosters. The boosters target two Omicron subvariants, BA.4 and BA.5.
While the original mRNA coronavirus vaccines have proven effective at preventing death and severe disease from COVID-19, breakthrough infections and reinfections have become more common in the face of an evolving virus.
Since the updated boosters (one from Pfizer-BioNTech and the other from Moderna) were granted an FDA emergency use authorization (EUA), the FDA and CDC have approved them for children, starting at age 6 months.
We asked Yale Medicine infectious diseases experts to answer common questions about these new, reformulated boosters.
The new booster is a bivalent vaccine, which means it contains two messenger RNA (mRNA) components of the coronavirus. Half of the vaccine targets the original strain, and the other half targets the BA.4 and BA.5 Omicron subvariant lineages, which are predicted to continue circulating this fall and winter.
The vaccines were authorized by regulators based on safety and effectiveness data from the original COVID-19 mRNA vaccines, as well as trials of the new formulation in mice. Regulators also took into account data from human trials by Pfizer and Moderna of a similar reformulation, aimed at a previous version of Omicron, BA.1.
In November, Pfizer released updated clinical trial data showing that the bivalent booster’s safety and tolerability in human adults remained favorable and similar to its original COVID-19 vaccine. Likewise, Moderna reported no new safety concerns in its human trials compared to its monovalent vaccine.
In mid-December, the CDC put out new data from two studies that suggest the bivalent boosters offer significant protection against illness and hospitalization. In the first study, 798 patients ages 65 and up received one dose of a bivalent booster in addition to at least two doses of the original, monovalent vaccines. Those who received the bivalent vaccine were 84% less likely to be hospitalized for COVID-19 than those who were unvaccinated and 73% less likely to be hospitalized than those who received two or more doses of the monovalent vaccine.
This study was conducted from Sept. 8 through Nov. 30, during a period of Omicron subvariant BA.5 or BQ.1.1 predominance.
In the second study, adults 18 and older who received a bivalent booster were 57% less likely to seek care at an emergency department or urgent care clinic compared to those who were unvaccinated. And those with the bivalent booster were 38% less likely to seek such care than those who received monovalent vaccination only with the last dose five to seven months earlier and 45% less likely than those who had monovalent vaccination only with the last dose 11 months earlier or more.
The study took place from Sept. 13 through Nov. 18, when Omicron subvariant BA.5 predominated and additional Omicron sublineages emerged.
The information from both studies came from comparisons of databases the CDC uses to track real-world effectiveness of vaccines. Neither were randomized controlled trials. Because the original monovalent booster is no longer available, the studies could not compare the bivalent and monovalent vaccines head-to-head during the same period of time.
The CDC recommends the new vaccine as a single booster dose at least two months following your most recent COVID-19 vaccine (whether it was completing two doses of a primary series or a booster). 
The FDA set the minimum wait time at two months. But some advisers to the CDC said it may be better to wait longer. Some health experts have suggested that more time between boosters—up to six months—might be preferred. 
That’s because someone who recently got a booster already has more virus-fighting antibodies in their bloodstream. Antibodies gradually wane over time, and another shot too soon won’t offer much extra benefit.
According to the CDC, if you recently had COVID-19, you may consider delaying your next vaccine dose by three months from the date your symptoms started—or, if you had no symptoms, when you first received a positive test. Studies have shown that increased time between infection and vaccination may improve your immune response.  
Reinfection, although possible, is also less likely in the weeks to months after infection. However, certain factors, such as personal risk of severe disease and local COVID-19 community level, could be reasons to get a vaccine sooner rather than later.
According to Pfizer, the company is working toward preparing an application for a bivalent vaccine for children ages 6 months through 4 years.
The old, monovalent Pfizer vaccine is no longer authorized as a booster dose for children ages 5 through 11 years, and the new bivalent boosters have not been approved for children younger than 5 years.

Yes, it’s fine to get the flu vaccine—as well as any other vaccine—and the new booster at the same time, Dr. Murray says. 
“Historically, we try to time the flu vaccine for October to maximize immunity when the flu peaks in the winter,” Dr. Roberts says. “But the flu season has been changing in the past few years, which means predictions will be much harder this year.”
Dr. Murray agrees. “Unfortunately for the flu shot, you never know the best time to get vaccinated until after flu season,” he says. “But influenza is circulating now in the community. So, it’s a good idea not to wait too long.” 
Yes, both bivalent vaccines are now authorized for children six months of age and up.
It’s really a personal decision, say the doctors.
“If you haven’t been boosted in the last couple of months, this is a great opportunity to be better protected,” Dr. Murray says. “Deciding on timing has a lot to do with your own health profile as well as that of those around you. If you’re with people who could become quite sick if you transmitted it to them, even if you had mild disease, that is something to consider.” 
Lifestyle also plays a role, Dr. Murray adds. “Some people wear masks; others do not. If you’re going on a cruise, I would recommend seriously thinking about getting that booster two weeks before you go,” Dr. Murray says. “If you don’t expose yourself to many large crowds or don’t go out to eat a lot, then you may choose to wait. But if it’s been more than 90 days since you’ve had COVID-19 or the booster, the benefits of getting this booster would outweigh any benefits from waiting.”
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