What we know about the latest COVID-19 variant XBB 1.5
In the battle against COVID-19, Omicron has proven to be difficult opponent. After emerging in other parts of the world, the variant of the SARS-CoV-2 virus that causes COVID-19 surfaced in the United States towards the end of 2021 and spread like wildfire. Since then, multiple Omicron subvariants have emerged, some of them more adept than others at evading immunity from vaccination or previous infection.
In early 2023, a new rising Omicron subvariant called XBB.1.5 appears to be the most transmissible strain of the virus so far. Cases are also believed to be rising with people spending more time in doors and attending recent holiday gatherings, with fewer wearing masks and taking other mitigation measures. Experts are still trying to better understand XBB.1.5 and other Omicron subvariants, such as BQ 1.1. and BA.5, which continue to circulate. They are also monitoring more than 300 other descendants of Omicron around the world.
Omicron: A 'variant of concern' with potentially different symptoms
First, some background. Omicron was initially identified in Botswana and South Africa in November 2021—although later reports showed earlier cases in the Netherlands. On December 1, the CDC confirmed the first case in the U.S., in an individual in California who had returned from South Africa in November. Omicron was the predominant strain in the U.S. by late December. As people around the world welcomed a new year, the variant continued to surge more quickly than any previous strain in many areas. Both the WHO and the CDC classified it as a "variant of concern."
Early reports from South Africa indicated that most cases were mild—and that symptoms for this variant seemed to be different. “The reports show that patients in South Africa—many of whom were young—have had severe fatigue, but no loss of taste or smell,” says Lauren Ferrante, MD, a Yale Medicine pulmonologist.
But some people infected with Omicron still developed severe disease and had to go to the hospital, and some died. For that reason, experts continued to express concerns that a large volume of cases in a particular area could overwhelm medical centers, making it difficult to treat severe cases.
Are Omicron and its strains more transmissible—or deadlier—than previous variants
From the beginning, two important questions about Omicron were top of mind for scientists, says Dr. Murray. As new variants have emerged, the first question has been how transmissible each one is compared to its predecessor.
According to the CDC, the Omicron variant spreads more easily than the original SARS-CoV-2 virus and the Delta variant. In its early days, the variant caused an alarming spike in COVID-19 cases in South Africa—they went from 300 a day in mid-November 2021 to 3,000 a day at the end of that month. In the first months of 2022, an Omicron subvariant called BA.2 began to spread even faster than other Omicron subvariants, followed by BA.4 and BA.5, only to be outdone by the BQ subvariants.
The second question has been whether Omicron and its subvariants are more likely than their predecessors to cause severe disease. While there is more to learn about the latest variants, experts are hoping prior immunity will be of some help. The original Omicron caused a record number of cases, but while it has also caused its share of hospitalizations and deaths, factors such as lengths of hospital stays, ICU admittance, and death were “lower than during previous pandemic peaks,” according to a CDC report in January 2022.
The CDC says the presence of severity of symptoms can be affected by vaccination, history of prior infection, and age and other health conditions.
Will Omicron be the last variant?
People need to understand that variants like Omicron are a natural part of the progression of the virus, Grubaugh says.
New variants aren’t surprising, he says. No one can predict how they might evolve—or if they will simply vanish at some point. “Delta was never going to be the last variant—and Omicron is not going to be the last one," Grubaugh says. "As long as there is a COVID-19 outbreak somewhere in the world, there is going to be something new that emerges.”