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Experts say Omicron boosters will more directly target the current variant. Luis Alvarez/Getty Images
  • Experts expect the common side effects of the new Omicron booster to be similar to previous COVID-19 shots.
  • The side effects include fatigue, headache, fever, skin redness, and muscle pain.
  • The experts note that the new booster might be more effective at preventing serious illness because it targets the current circulating variants more precisely.

The Omicron variant of COVID-19 has a somewhat different set of typical symptoms than other versions of the disease.

However, the possible side effects of new vaccines specifically targeting Omicron are not likely to differ from those associated with previous vaccines and boosters.

In August, the Food and Drug Administration (FDA) gave emergency-use authorization to a pair of new booster shots, developed by pharmaceutical companies Pfizer-BioNTech and Moderna. Each targets both the original strain of COVID-19 as well as the latest Omicron (BA.4 and BA.5) variants of the novel coronavirus.

“Having a more specific spike protein for the immune system to look for should make the vaccine more effective at preventing infection and severe disease with the currently circulating variants,” Kristen Nichols, PharmD, a senior content management consultant for the clinical effectiveness sector at healthcare consultants Wolters Kluwer, told Healthline. “Also, since the immune system will now recognize two similar variations, it may be more efficient at also recognizing new variants.”

The “bivalent” booster vaccines became available to the public in early September. That’s not long enough to compile real-world data on the boosters’ side effects. But clinical trial research submitted to the FDA found that side effects of the Omicron booster were similar to the symptoms of other COVID-19 vaccines.

The most common side effects from the Omicron BA.4 and BA.5 booster were pain at the injection site, fatigue, headache, joint and muscle pain, chills, axillary swelling and tenderness, nausea/vomiting, skin redness and swelling at the injection site, and fever.

Dr. Marisa Montecalvo, an infectious disease expert at NYC Health and Hospitals-Metropolitan and Westchester Medical Center, reported that “55 to 75 percent of people develop pain at the injection site, and a small percentage of people (5 percent) may have swelling or redness at the injection site.”

More serious but rare side effects of previous COVID-19 vaccines have included anaphylaxis and other severe allergic reactions, myocarditis, pericarditis, and fainting. FDA officials said it’s possible that similar problems could arise from the newest vaccine boosters as well.

“The risk of myocarditis/pericarditis is rare and continues, as with previous vaccines, to be seen primarily among adolescents and young adult males,” Montecalvo told Healthline.

“The risk after a booster dose appears to be lower than that after the primary series of vaccines,” she added.

There’s no reason to think that symptoms from the new booster would be different from previous COVID-19 vaccines and boosters, said Dr. Jason Gallagher, an infectious disease expert and clinical professor at Temple University’s School of Pharmacy and a clinical pharmacy specialist in infectious diseases at Temple University Hospital in Philadelphia.

“The only thing that changed is which proteins on the surface of the protein it encodes for,” Gallagher told Healthline. “All of the other components are the same and the side effects come from the immune response.”

“The typical side effects following a vaccination can be expected,” agreed Dr. Jose Mayorga, executive director of the University of California at Irvine Health’s Family Health Centers. “These include fatigue, sore arm, fever, and headache. The patients we have vaccinated in our clinic have had mild side effects that over-the-counter Tylenol or Motrin has relieved.”

“The only side effect I got from this vaccination was peace of mind,” Mayorga told Healthline. “I feel safer against serious disease.”

Gallagher said that additional data on side effects of the Omicron booster will be gathered as more people get the shot.

“I would not be surprised if the side effects are more intense, especially if you’ve been boosted for COVID recently or had COVID, because your immune system is already primed” to attack the virus, he said.

The Centers for Disease Control and Prevention (CDC) recommends waiting at least two months after a COVID vaccine or illness before getting a booster shot.

CDC officials also advise only getting a booster matching your initial doses of vaccine — a Moderna booster if you were vaccinated with the Moderna vaccine, for example.

Like other COVID-19 vaccines and boosters, the new Omicron booster should, at a minimum, protect recipients from serious illness and hospitalization. However, Gallagher noted that the new booster has the advantage of precisely targeting the dominant COVID-19 variant in circulation now.

“It could prevent some infection, too,” he said. “It’s a better match [to the virus] than we’ve had in a long time.”