The XBB1.5 COVID-19 variant: 7 questions, answered

A new COVID-19 subvariant called XBB1.5 is on the rise across the U.S.  

Early reports indicate that it is much more contagious than previous variants, and may be better at avoiding the immune system’s defenses. To learn more, we went to Chief Infection Control Officer Roy Chemaly, M.D.  

1. How is the XBB1.5 subvariant different from previous strains of COVID-19? 

XBB1.5 contains more mutations that allow it to better avoid the human immune system’s defenses. That means even if you’ve been fully vaccinated and boosted and/or had a previous COVID-19 infection, XBB1.5 may be able to find a way around that to cause an infection anyway. So, it is more transmissible than any other variant. That’s what initially got our attention. 

The XBB1.5 subvariant is able to bind to human cell receptors much more efficiently. So, while previous variants took about 4 to 6 weeks to spread widely enough to become one of the most frequently found strains among confirmed cases, this one only took a couple of weeks.

As of Jan. 9, COVID-19 caused by the XBB1.5 subvariant accounted for about 25% of confirmed new cases in the U.S. 

2. Does the XBB1.5 subvariant make people sicker than previous variants?

It’s too early to say for sure, but XBB1.5 doesn’t appear to cause more severe illness than previous COVID-19 strains. It’s probably not going to be as bad as the delta variant since we’re not seeing higher rates of severe infection or hospitalization so far.

3. Do you anticipate a surge in cases caused by XBB1.5?

It’s too early to tell yet, but there are indications that this one might not be as bad. The worst surge by far was from omicron. I don’t think this one will be the same. 

I suspect that any surge we get from the XBB1.5 subvariant will be closer to the type we had with BA.4 and BA.5 this past summer. Both produced slow increases in the number of cases and then equally slow declines.

4. Do the current COVID-19 vaccines provide protection against XBB1.5? 

Absolutely. Getting a COVID-19 booster is still highly recommended. But remember: the goal of COVID-19 vaccines and boosters is not only to prevent infection. That would be unrealistic. The goal is to prevent severe infections that require hospitalization. And the current vaccines and boosters should still do that against the XBB1.5 subvariant.

5. Why should cancer patients and their caregivers pay particularly close attention to XBB1.5?

XBB1.5 is highly transmissible — and possibly the most transmissible subvariant so far, based on lab studies. That’s due to the specific mutations this one acquired, which make it much more contagious.

That’s why patients should make sure they’re fully vaccinated and boosted. That way, if you do catch it, you may still get sick, but you probably won’t die or be hospitalized. And even partial protection against severe infection and hospitalization is better than none.

6. Do the COVID-19 treatments work against XBB1.5? 

Yes, the oral or IV drugs we use to treat COVID-19, such as paxlovid and remdesivir, still work.

The monoclonal antibodies used to prevent infection, such as EVUSHELD, don’t work as well against XBB1.5. 

7. Any special guidance for immunocompromised people?

Because XBB1.5 is very contagious — and the flu, RSV and other respiratory viruses are still circulating — anyone who is immunocompromised should be extra vigilant about masking right now. Give yourself an added layer of protection by wearing a face mask any time you’re out in the community. 

Your first and best line of defense right now against COVID-19 is the vaccines, including the new bivalent boosters. But your second line of defense is masking. 

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