Fragmented COVID-19 microbes in turquoise and white.
Illustration: PGN

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What you need to know

  • XBB.1.5 is the most transmissible COVID-19 strain yet, can evade previous immunity, and is resistant to many of our existing drugs and treatments.
  • Antiviral treatments Paxlovid, remdesivir, and molnupiravir continue to work.
  • Stay up to date on vaccinations, wear N95 masks, and seek available treatments to protect against XBB.1.5.

After spreading in the U.S. for a couple of months, Omicron subvariant XBB.1.5 became the country’s dominant COVID-19 virus strain in late January. The highly transmissible strain now makes up about 60 percent of circulating COVID-19 viruses in the U.S. and is especially prevalent in the Northeast. But its fast-spreading nature isn’t its only strength.

What is XBB.1.5, and should we be concerned?

The most transmissible COVID-19 strain yet, XBB.1.5 is under the XBB lineage, which is a recombinant that appeared after a human became simultaneously infected with BA.2.10.1 and BA.2.75. The good news is that after a relatively mild rise in COVID-19 cases, hospitalizations, and deaths around the holiday season, COVID-19 seems to be in decline once again. But XBB.1.5 is still worrisome, especially for individuals at high risk of severe disease, because it can evade previous immunity and is resistant to many of our existing drugs and treatments.

What COVID-19 treatments no longer work? 

The FDA withdrew its authorization of Evusheld last week because the drug is not effective against more than 90 percent of currently circulating COVID-19 viruses. Evusheld was an antibody drug that immunocompromised people, who receive less protection from vaccines, could take as an added layer of protection against COVID-19 infection. In November, the FDA pulled its authorization of antibody treatment bebtelovimab, also because it no longer works against more recent Omicron subvariants.

What COVID-19 treatments are still available?

Antiviral treatments Paxlovid, remdesivir, and molnupiravir continue to be authorized by the FDA. Each of these options needs to be taken within days of when symptoms start. Some immunocompromised individuals may not be able to take Paxlovid, as it does not interact well with certain drugs. Another option for immunocompromised people is convalescent plasma, which uses blood that is high in antibodies from donors who have recovered from COVID-19.

What else can high-risk people do to stay safe?

Even though Evusheld is no longer effective, people with weakened immune systems still have many ways to protect themselves against XBB.1.5. First of all, stay up to date with COVID-19 vaccinations. Studies and real-world data have shown that bivalent boosters provide extra protection against XBB.1.5 infection and significantly reduce the risk of hospitalization. Wearing high-quality masks and improving indoor ventilation are both effective ways to protect against infection. And finally, talk to your doctor now about COVID-19 treatment options available to you so that you are prepared in case you get infected.