If you’re considering getting an omicron-specific Covid booster shot, you might be wondering what its side effects are – and how serious.
Rest assured, they shouldn’t be much different from what you may have experienced with previous vaccine and booster doses.
“We just don’t have any data on that. [yet]essentially giving two vaccines in one injection – but biologically I just wouldn’t expect the side effects, severity or safety profile of the injections to be any different from current mRNA vaccines and boosters,” said said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia and a member of an independent advisory panel for the United States Food and Drug Administration, told CNBC Make It.
The reformulated injections from Pfizer and Moderna are bivalent, meaning they target both the original Covid strain and the BA.5 and BA.4 subvariants of omicron. Side effect data is not yet available because the new boosters were approved by the FDA and the Centers for Disease Control and Prevention before completing their clinical trials.
Federal agencies based their approvals on several other safety data, including evidence from the original Covid vaccines – the updated formulations are just a modification of those originals – and laboratory data on the BA.5 element. injections in mice.
They also reviewed clinical trial data on earlier versions of bivalent boosters targeting the BA.1 subvariant of omicron. These snaps were never released to the public, as BA.1 was quickly overtaken by other omicron sub-variants – but their design is extremely similar to the snaps now available in pharmacies and clinics nationwide.
Together, the evidence shows a potential roadmap for the side effects you can expect after receiving one of the new boosters, and the severity of those side effects.
Expected side effects
In the Pfizer and Moderna clinical trials for BA.1 injections, participants who were already fully vaccinated with a booster shot received an updated booster dose. In both clinical trials, the most commonly reported side effects within seven days of injection were:
- Muscle pain
- Articular pain
- Redness and swelling at the injection site
It’s a familiar list: it’s the same group of side effects that came with the original formulations. Importantly, in these clinical trials, the severity of side effects was very mild.
The Pfizer trial found that approximately 52% of participants who received the BA.1 vaccine experienced mild pain at the injection site, 8% experienced moderate pain, and only 0.3% experienced severe pain . About 26% of participants experienced a mild or moderate headache, while only 0.3% experienced a severe one.
Moderna’s trial found that nearly 59% of participants had fatigue, but only about 4% had fatigue at the Grade 3 level, which is defined as significant fatigue that interferes with daily activity.
Serious side effects are “usually” most common after receiving a second dose of a vaccine, not after receiving a third or fourth dose, says Offit. You are only eligible for new boosters if you have completed a series of primary vaccinations, which means most people will have already received at least two doses in advance.
The same concept held true in the last set of recalls. The new vaccines have the same doses as the original vaccines, which further suggests that their safety profiles may be similar, Offit says.
A single dose of Pfizer’s monovalent vaccine contains 30 micrograms of mRNA targeting the original Covid strain. The updated booster shots contain the same number of micrograms, 15 targeting the original strain and the remaining 15 targeting BA.4 and BA.5.
The monovalent dose of Moderna contains 50 micrograms of mRNA per dose targeting the parent strain. Its updated booster contains 25 micrograms targeting the original strain and 25 targeting the omicron subvariants.
The BA.1 trials tested only a few hundred people, which is a relatively small sample size compared to the thousands of Americans expected to receive the new BA.5 doses, Offit notes. You can still be confident going in, he says – but not 100% sure what to expect.
“We need to keep our eyes wide open for side effects and adverse events that may arise, while keeping in mind that this is a new product,” says Offit.
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