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What We Know So Far About the XBB.1.5 COVID Variant in Wisconsin

lab scientist holding a COVID vial

What Is XBB.1.5 and Are You Still Protected by Current Vaccines?

By Sarah Wilczek, pharmacist at Network Health

That’s right. Another COVID variant has hit the news, ringing alarm bells across the country. We’re talking about the XBB.1.5 variant, and to be more precise, it is actually a subvariant of the Omicron COVID-19 variant that was first classified by the World Health Organization (WHO) back in November 2021. Now, WHO staff are saying XBB.1.5 is the most transmissible form of Omicron that we have seen yet.

The folks here at Network Health are here to inform and not spark fear, however, so let’s take a step back and consider what we know. With clear information, you can come to a reasonable conclusion about XBB.1.5’s severity and how to best protect yourself.

How Prevalent Is XBB.1.5?

Numbers surrounding XBB.1.5’s prevalence have been somewhat unclear. Recently, the Centers for Disease Control and Prevention estimated that the strain was responsible for 40.5 percent of confirmed U.S. cases before changing that number to just 18.3 percent.

What we do know for certain, however, is that XBB.1.5 is spreading. It is the only Omicron subvariant that is showing growth in the U.S. That said, it is not yet the dominant form. That title belongs to BQ.1.1, another subvariant of the Omicron strain. The concentration of XBB.1.5 varies widely from region to region, with some states seeing a far higher prevalence than others.

Is XBB.1.5 In Wisconsin Yet?

For those here in Wisconsin, XBB.1.5 has already shown up in the state. In fact, according to the Wisconsin State Laboratory of Hygiene, it’s been in the state since late September 2022.

The laboratory doesn’t teste very single COVID-19 case, though. Only a small percent of the total cases in Wisconsin are tested, meaning XBB.1.5 may be more prevalent than we know and may have appeared in the state even earlier. So far, however, confirmed cases of XBB.1.5 have been discovered in Polk, Winnebago, Dane, Waukesha and Milwaukee Counties.

Do COVID-19 Vaccine Boosters Work Against XBB.1.5?

If you’ve received a COVID-19 booster, you may wonder whether it will still protect you against this new Omicron subvariant. Studies suggest that the bivalent vaccine, which was designed particularly to protect against Omicron strains, is still effective at protecting against severe disease. It may not protect against infection, though.

The bivalent boosters have been available for a few months but booster rates in Wisconsin have room for improvement. Just 18 percent of those eligible in Wisconsin have received the updated bivalent booster. This rate improves to 42 percent when looking at just those age 65 and older.

There is much to learn about the new XBB.1.5 Omicron subvariant, but as has been the case, the best course of action to stay protected is to get vaccinated and get boosted. To find a vaccination site near you, go to


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