Do Bivalent Boosters Protect Against XBB.1.5?

As of mid-January 2023, the XBB.1.5 subvariant is responsible for nearly half of all COVID-19 cases in the United States. According to the World Health Organization (WHO), XBB 1.5 is the most transmissible Omicron subvariant yet.

Researchers are trying to figure out how we might need to change our public health strategies for combatting COVID, including vaccines and boosters, to fight XBB, as well as any future variants.

Here's what experts want you to know about the new bivalent COVID boosters and XBB.1.5.

Why XBB.1.5 Is Tricky to Fight

XBB 1.5's rapid spread suggests that the virus has changed in ways that make it better at evading immune responses—and that means the measures we need to take to fight it might have to change too.

For example, the Food and Drug Administration (FDA) recently announced that it does not think that Evusheld (pre-exposure prophylaxis to prevent COVID) will work against XBB.1.5. However, the agency is waiting on more data to confirm whether the medication could protect people who are exposed to the virus later.

Do Bivalent Boosters Work Against XBB1.5?

Mark Loafman, MD, MPH, a family physician and chair of the Family and Community Medicine Department at Cook County Health, told Verywell that there is reason to worry "that variants will continue to evolve with increasing ability to evade the vaccine," but that "fortunately, the mRNA vaccine technology allows a relatively rapid response to that if it occurs.”

Early research is showing that the updated COVID vaccines with Omicron BA.5 spike proteins in them may provide protection against XBB.1.5.

According to a small study published in The New England Journal of Medicine, the bivalent vaccines produced neutralizing antibodies against XBB. The people who got the bivalent boosters had better neutralizing activity than people who got either one or two monovalent boosters.

Are Bivalent Boosters Better than Original Vaccines?

Irfan Hafiz, MD, infectious diseases expert and chief medical officer at the Northwestern Medicine Huntley, McHenry, and Woodstock Hospitals in Illinois, told Verywell that these findings mean that at least in a lab setting, antibodies produced by the bivalent COVID vaccine do appear to bind to the XBB variant.

Therefore, Hafiz said that the updated bivalent vaccine "should offer greater immunity [against XBB.1.5] than the original vaccination.”

Another preprint study also suggested that the bivalent booster is more immunogenic—meaning it prompts an immune response—than monovalent boosters against the Omicron subvariants that are going around, including XBB.1.5.

While more research and larger studies are needed, it seems that bivalent boosters are capable of providing significant protection against this variant.

Will There Be an XBB.1.5 Surge?

It looks like XBB is more contagious than previous variants, but doesn't cause more severe disease—at least when you look at the number of hospitalizations. According to Hafiz, it's possible that at-risk people who get it may not get seriously ill.

Loafman agreed that the trend with new variants seems to be that they're infecting people better, but not necessarily making them sicker.

According to Loafman, higher infectivity is why a new variant quickly becomes the dominant cause of COVID in a given geographical area. That said, even if most of those illnesses aren't severe enough to put people in the hospital, it doesn't mean we can stop worrying about COVID.

"We still have hundreds of deaths from COVID every day," said Loafman. "So we should not let the small improvement in severity be a cause to let our guard down."

What You Can Do

According to Hafiz, it's hard to say how a potential XBB.1.5 surge might compare to the BA.5 subvariant or the original Omicron variant at its peak. Here are some factors that we know drive COVID surges:

• More transmissible variants
• Lower bivalent vaccination rates
• More travel and indoor group activities
• Less frequent use of masking

Experts recommend that you get boosted as soon as you're eligible. However, according to the Centers for Disease Control and Prevention (CDC), only about 15% of the U.S. population has received a bivalent booster dose.

Once you're caught up on vaccines, Hafiz said that “monitoring community rates and masking in crowded settings will help reduce the [infecton] risk" of COVID moving forward.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.