As we've learned over the last year, COVID-19 variants are to be expected.

Thankfully, the mRNA technology powering our COVID-19 vaccines provides us with a way to respond when variants not only arise but predominate, as is the case with the highly infectious omicron variant.

Evidence of this are the updated Pfizer and Moderna COVID-19 vaccine boosters targeting the omicron variant. They were authorized for use in teens and adults by the FDA and CDC in late August. The agencies also recently expanded this authorization to include children five years of age and older.

"The BA.5 omicron strain now makes up the vast majority of COVID-19 cases across the U.S.," says Dr. H. Dirk Sostman, chief academic officer of Houston Methodist. "The updated vaccines are specifically designed to increase immunity to this variant, reducing symptom severity and the chance of severe disease."

They come at the perfect time, as some experts are predicting that another wave of COVID-19 could hit hard this upcoming fall and winter.

How do the updated vaccines differ from the original ones?

The FDA has been incredibly deliberate in referring to the vaccines as "updated" rather than "new," and there's an important reason for that.

They're different from the original vaccines in just one small, albeit powerful, way.

"The updated vaccines use the same technology as the existing ones, meaning they work the same way," says Dr. John Cooke, medical director of the RNA Therapeutics Program at Houston Methodist. "They simply now contain two mRNA molecules instead of just one."

Recall that the Pfizer and Moderna COVID-19 vaccines are mRNA vaccines, meaning they use pieces of mRNA to help train your your immune system to recognize viral proteins — the spike protein on the virus' surface, in particular. This helps your body mount a quicker and more efficient immune response to the virus should you get infected. (Related: How mRNA COVID-19 Vaccines Work)

"In addition to containing mRNA encoding a piece of the original virus' spike protein, the updated vaccines include a second piece of mRNA encoding the spike protein of the BA.4/BA.5 omicron variants," explains Dr. Cooke. "It's a small adjustment from a technological standpoint, but a powerful one in terms of how it can help boost immunity to the specific variants currently circulating."

This dual nature is why the updated vaccines are referred to as bivalent.

"They are called bivalent vaccines because half of the booster targets the original COVID-19 virus, and the other half works against the omicron variant," adds Dr. Sostman.

How effective is the booster against omicron?

"Based on the data supporting their authorizations, the bivalent COVID-19 vaccines are expected to provide increased protection against the currently circulating omicron variant," says Dr. Sostman.

Human clinical trials of the updated boosters are still ongoing. But while the real-world effectiveness of these vaccines isn't fully known just yet, there are no concerns over safety.

"FDA officials say that the public can rest assured that a great deal of care has been taken to ensure that the updated vaccines meet the agency's rigorous safety, effectiveness and manufacturing quality standards for emergency use authorization (EUA)," explains Dr. Sostman.

COVID-19 vaccines are estimated to have saved almost 20 million lives in 2021 alone. The technology is already proven to be safe and effective.

"Officials explained in a press conference that they have extensive experience with strain changes for annual influenza vaccines, which also do not require clinical trials," adds Dr. Sostman. "In fact, the ability to tailor a vaccine to the currently circulating viral variant is one of the great advantages of the mRNA vaccine technology."

Similar to influenza, SARS-CoV-2 has proven to be capable of change — and like flu shots, the COVID-19 vaccines will likely continue to be adapted to whichever variants are currently circulating.

"It's not clear yet how often boosters will be needed, but many experts say it's reasonable to expect that — at least for the next few years while we continue to build the 'immunity wall' against COVID-19 — COVID-19 shots could be given on an annual schedule like the flu shot, a vaccine we're already accustomed to changing yearly," says Dr. Sostman.

Who is eligible for the omicron booster right now?

"The bivalent COVID-19 vaccine boosters are authorized as a single dose in people who have completed their primary vaccination series, as well as those who have also received one or more booster shot already," explains Dr. Sostman.

Though, if you've recently received a booster dose of the original vaccine or you've recently had COVID-19, you may not be eligible for the updated booster just yet. More on this in a moment.

Age matters, too:

• Adults 18+ can receive either the Pfizer or Moderna bivalent COVID-19 booster vaccine
• Teens ages 12-17 can receive either the Pfizer or Moderna bivalent COVID-19 booster vaccine
• Kids 5+ can receive the Pfizer bivalent COVID-19 booster vaccine
• Kids 6+ can receive either the Pfizer or Moderna bivalent COVID-19 booster vaccine
• Children younger than 5 are not yet eligible
  
  

How long should I wait if I recently received a booster shot?

"According to the FDA, you should wait until at least two months have passed since your last booster vaccination to receive the updated booster," says Dr. Sostman.

This also applies to those who recently completed their primary vaccine series — you will need to wait at least two months before getting the omicron booster.

"Some experts think it's beneficial to wait even longer," adds Dr. Sostman.

Do I need to get the updated booster if I just had COVID-19?

Many people recently recovering from COVID-19 are likely wondering whether they'll even need the updated booster.

"There are many unknowns about natural immunity to COVID-19, including how long you can expect it to protect you," says Dr. Sostman. "For this reason, relying only on natural immunity without the vaccine-based immunity isn't recommended."

That said, the FDA and CDC have recommended that people recently infected with COVID-19 should wait at least three months post-infection before being vaccinated with the omicron booster. However, individual factors such as risk of severe COVID-19 disease or community outbreaks should be taken into account when determining timing of booster vaccination after infection.

How can I get the omicron booster?