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What We Know About The ‘Arcturus’ COVID Strain

A girl gets the COVID vaccine on her right arm from a health expert. Both have their faces covered.
Zelena Nicole Camargo Castellanos, 10, receives a vaccine dose at a media event that kicked off COVID-19 vaccinations for children ages 5-11 in Los Angeles County in 2021.
(Alborz Kamalizad
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A coronavirus variant anecdotally linked to pinkeye and increased COVID-19 cases in children is spreading in Los Angeles County, but experts are not yet sounding the alarm.

The highly contagious variant was first discovered in India. Last week, the World Health Organization elevated the fast-growing Omicron sublineage XBB.1.16 as a new variant of interest, and says it is outcompeting the previously dominant XBB.1.5 in many regions of the world, though not yet in the United States.

The variant XBB.1.16 has been nicknamed "Arcturus" on social media. Here’s what we know about it.

Is this strain cause for concern?

Last week in the United States, XBB.1.16 accounted for an estimated 10% of COVID cases nationally, up from about 6% the week prior. The XBB.1.5 variant continues to be the dominant cause of new infections in the United States, according to data from the Centers for Disease Control and Prevention.

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A similar situation is playing out in L.A. County. XBB.1.16 is growing, and now accounts for just over 1% of sequenced cases in the county. The percentage is expected to continue to increase, said L.A. County Public Health Director Barbara Ferrer at a press conference last week. There are at least 10 coronavirus strains circulating in L.A. County, with the dominant XBB.1.5 still accounting for 71% of cases.

A slide detailing updated COVID vaccine guidance by age group.
Courtesy of the L.A. County Department of Public Health)

“We can anticipate the possibility that one of the newly circulating strains can become dominant based on past experience. As new strains become dominant, there's an increased potential for infection or severe illness and possibly new,” Ferrer said. “Because of this, it's important that we do monitor our local conditions while we look at the data from other parts of the world and our country.”

Link to pinkeye

Most of the information we know about XBB.1.16 has come out of India, where it was first detected. It's being reported that this strain is infecting young children more, and that conjunctivitis or pinkeye may be more common.

“Previously, conjunctivitis has been reported in about 1 to 3% of COVID cases, so it's rare, but not unheard of,” Ferrer said.

She cautioned that it’s too early to say definitively if XBB.1.16 is associated with more pinkeye in children and that people shouldn’t use it as a defining symptom of COVID.

“It’s important for those people who do have conjunctivitis or are caring for children with conjunctivitis to seek medical care. We'll be monitoring this obviously as we move forward,” Ferrer said.

Call public health center at 1-833-540-0473 to get vaccinated.
Courtesy of the L.A. County Dept. of Public Health )

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How is XBB.1.16 different from other strains?

XBB.1.16 is a descendant of XBB, which is a mashup of two BA.2 sublineages. It is the dominant variant in India, where it is causing a wave of illnesses. It has been detected in 32 other countries, including the United States.

This offshoot is very closely related to XBB.1.5, the dominant strain in the U.S. and L.A. County. It has two gene changes that are different, including one in its spike protein, said Paula Cannon, a virologist at Keck School of Medicine of USC.

“It's different, but not that different from what we currently have. Having said that, omicron is the absolute star of these different COVID variants in terms of being able to dodge our immune responses,” Cannon said. “Even though it's incredibly similar to XBB.1.5, which is the current winning strain, even if you've had XBB.1.5, that is not going to protect you from getting XBB.1.16.”

Cannon said that whether a variant will cause a wave of cases in a country depends on the immunity in the population as well as the variant that was last the dominant cause of infections there.

“Timing is a big part of it. If your country has just had a really big outbreak of the virus with a different variant then there's much more recent immunity in the population to protect people against the next wave,” Cannon said. “People got a little booster in the new year, whether they wanted it or not, and I think that's going to protect us as a population from having a wave like they're currently seeing in India.”

The WHO says while this variant seems to be spreading faster than previous variants, and escapes immunity — even in people who’ve recently had the XBB.1.5 strain — it does not seem to be causing more severe illness.

“The good news is that because all of these new strains are descendants of the omicron variant, our vaccines and our therapeutics are likely to remain highly protective and able to ward off severe illness,” said Ferrer. “Studies and clinical data provide a mountain of evidence on the effectiveness of the bivalent booster at reducing the risk of symptomatic infection and severe illness,” said Ferrer.

A bar graph showing children are the least vaccinated in L.A. County.
Courtesy of the L.A. County Dept. of Public Health)

Cannon explained the importance of getting at least one dose of the bivalent COVID vaccine as XBB.1.16 continues to spread.

“We have very powerful real-world data that's coming out, showing that when you compare people who got the bivalent versus people who [were only vaccinated with the original vaccines] there's a huge difference in the level of protection people got from serious illness and hospitalization and death. It's really very striking,” she said. “The bivalent is an evolved next-generation vaccine that is more like the viruses that are circulating. So it makes sense that it should have a better effect.”

Bivalent vaccine uptake has been low in L.A. County. Children remain the least vaccinated age group with less than 15% of eligible children 5-17 receiving the shot. The most vaccinated age group is also the most vulnerable — just 45% of people 65 and older have received the shot.

What’s the overall COVID situation in LA?

This week’s COVID cases overall decreased slightly to 2,659 compared to 3,114 last week in L.A. County. A Public Health press release said “the small increase in wastewater concentrations of SARS-COV-2 this week may reflect the beginning of more spread associated with [XBB.1.16] a new strain of Omicron.”

The seven-day average number of COVID hospitalizations is 275 this week, a decrease from 328 last week, while reported weekly deaths increased slightly from 44 last week to 54 this week.

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