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Omicron has been the dominant COVID-19 variant in the U.S. for months, but it’s spawned several subvariants that have caused spikes in cases. Now, there are two new subvariants infectious disease experts are keeping an eye on: BA.4 and BA.5.

While data from the Centers for Disease Control and Prevention (CDC) show that the Omicron subvariant BA.2.12.1 (Stealth Omicron) is the current dominant form of COVID-19 circulating in the U.S., data from viral surveillance organization Helix shows that BA.4 and BA.5 now represent up to 7% of new COVID-19 cases. And that’s a percentage that seems to be growing.

Omicron subvariants are nothing new but, historically speaking, the rise of a new subvariant—let alone two subvariants—seems to correlate with an increase in COVID-19 cases.

Here’s what you need to know about Omicron subvariants BA.4 and BA.5, including where the new subvariants first appeared, the symptoms, and how concerned you should be.

What are the symptoms of BA.4 and BA.5?

As a whole, the symptoms of COVID-19 have stayed fairly consistent, and BA.4 and BA.5 don’t seem to be a big departure from other Omicron symptoms, says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York. “They also seem to cause no more or less severe disease than earlier renditions of Omicron,” he adds.

The most common symptoms of COVID-19, per the CDC, include:

  • Fever or chills
  • Cough
  • Shortness of breath or difficulty breathing
  • Fatigue
  • Muscle or body aches
  • Headache
  • New loss of taste or smell
  • Sore throat
  • Congestion or runny nose
  • Nausea or vomiting
  • Diarrhea

    But a CDC report published in December found that patients with Omicron generally have these symptoms:

    • Cough
    • Fatigue
    • Congestion
    • Runny nose

      Where did BA.4 and BA.5 originate?

      It’s not entirely clear where BA.4 and BA.5 originated, but they’ve been detected at low levels in several countries in Southern Africa and Europe, according to the World Health Organization (WHO).

      WHO’s technical lead on COVID-19, Maria Van Kerkhove, said in May that the variants have been spotted in Botswana, South Africa, Germany, and Denmark, among other countries.

      Do tests detect the new subvariants?

      Yes, COVID-19 tests are able to detect the new variants, says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine.

      One thing to note, per Dr. Russo: While BA.2 had certain genetic traits that made it harder to classify as Omicron on polymerase chain-reaction (PCR) tests, that doesn’t seem to be the case with BA.4 and BA.5.

      “That’s a quick and dirty way to find out if BA.4 and BA.5 are circulating if you’re in a BA.2-dominant region,” he says.

      How do these subvariants differ from BA.2.12.1?

      BA.4 and BA.5 have mutations that make them slightly different from BA.2.12.1. “There’s a pattern here,” Dr. Schaffner says. “We had Omicron and then there are Omicron mutations that were as contagious or even more contagious than Omicron. It’s a continuing story.”

      BA.4 and BA.5 “are more closely related to BA.2 and its subvariants than to BA.1,” Dr. Russo says. BA.4 and BA.5 have an amino acid change that was present in the Delta variant, Dr. Russo says. “Because of this, there’s some speculation that, if you were infected with Delta, it may help you out with BA.4 and BA.5,” he says.

      What can people do to protect themselves?

      Dr. Russo recommends sticking to “the usual” prevention methods. That means getting vaccinated against COVID-19, if you haven’t already, and making sure you’re up to date on your boosters.

      “Vaccine-induced immunity seems imperfect at preventing infection, but it looks like it will do a good job at keeping people out of the hospital with severe disease,” he says.

      And, if you’re considered at high-risk for complications from COVID-19, he also suggests wearing a “high-quality, well-fitting mask” in indoor settings.

      Overall, experts say that public health officials are keeping an eye on BA.4 and BA.5. “These variants are something that we in public health are watching,” Dr. Schaffner says.

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