The XBB.1.5 Variant in New York City, Late 2022: Faster Spread, No Sign of Worse Illness

A variant that took off in New York City

The Omicron XBB.1.5 variant — a recombinant of Omicron BA.2.75 and BA.2.10 — was first detected in New York City in October 2022. By January 7, 2023, it made up 81% of sequenced specimens in the city, against only 26% nationwide; in December, just 5% of sequenced genomes in the rest of New York State were XBB.1.5. The city was likely the epicenter of its U.S. emergence.

The World Health Organization noted that XBB.1.5 carries no mutation known to change severity — such as the Delta spike mutation P681R — but data on severity in people were limited. Because the variant arrived in New York City early, and the city's Department of Health and Mental Hygiene routinely links genome sequencing with case data, it was well placed to study it.

How it was studied

Samples from city residents — from five health department COVID-19 Express labs, 190 outpatient clinics and 11 emergency departments across all five boroughs in the city's public hospital system — were sequenced at the department's Public Health Laboratory or the Pandemic Response Laboratory. Results were matched to the city's COVID-19 surveillance database, immunization registry, health information exchanges and death registry for demographics, earlier positive tests, monovalent vaccination history, hospitalization and deaths.

The comparison: 3,019 people infected with XBB.1.5 versus 6,067 infected with BQ.1 (and its descendants), from November 1, 2022, to January 4, 2023. The two were circulating together from November, and BQ.1 was dominant when XBB.1.5 appeared.

What was found

From November to December 2022, XBB.1.5's share of sequenced samples in the city rose from 8% to 72%. Compared with BQ.1 patients, XBB.1.5 patients were:

There was no difference in the share hospitalized or who died — no sign that XBB.1.5 caused more severe disease.

Caveats

• Sequenced patients were only 4%–12% of lab-confirmed cases in the city in November and December 2022, and they differed from the rest: more were aged 18–64 (74% vs. 68%), lived in high-poverty neighborhoods (42% vs. 37%) and in Brooklyn (35% vs. 29%), were Black (28% vs. 20%), or were hospitalized (7% vs. 6%). The share who died was the same (1%) either way.
• Bivalent booster data had not yet been matched to the surveillance database.
• The findings are preliminary and may change as more data come in.

Why it matters

Even though only a small share of cases are sequenced, linking genomic and case data lets health departments size up new variants quickly — including how severe they are — and keep tracking reinfection, infection after vaccination and disease severity over time.

Sources

Based on Elizabeth Luoma, Rebecca Rohrer, Hilary Parton and others (New York City Department of Health and Mental Hygiene), "Notes from the Field: Epidemiologic Characteristics of SARS-CoV-2 Recombinant Variant XBB.1.5 — New York City, November 1, 2022–January 4, 2023," MMWR, Centers for Disease Control and Prevention; published by CDC and in the public domain; rewritten in hubnx's own words. The report calls the rise from 8% to 72% "eightfold"; this page gives the two figures.