A new Omicron subvariant of COVID-19 known as JN.1 has rapidly spread across the United States, accounting for nearly half of all new cases over the past week. According to the latest data from the Centers for Disease Control and Prevention (CDC), the JN.1 variant made up over 39% of U.S. COVID-19 cases in the week leading up to December 24th [1]. This is a significant increase from earlier in December when JN.1 accounted for less than 8% of sequenced cases nationwide.
Key Facts About the JN.1 Variant
- JN.1 is an Omicron subvariant that emerged in recent months as an offshoot of the BA.5 lineage. It carries additional mutations in the spike protein that may enable greater immune evasion.
- Since mid-December, JN.1 has rapidly overtaken other Omicron subvariants to become the dominant strain in the U.S.
- As of December 24th, JN.1 caused an estimated 43.6% of COVID-19 cases nationwide over the preceding week [2].
- Early data suggests JN.1 is even more transmissible than other Omicron variants, fueling a new wave of infections.
- So far, JN.1 infections seem to cause less severe illness on average, but more data is needed.
JN.1 Fueling Rise in Infections After Holidays
The rapid ascent of JN.1 comes on the heels of holiday gatherings, travel, and indoor events that facilitate transmission of respiratory viruses. Preliminary data indicates that JN.1 is even more contagious than earlier Omicron variants, with CDC models estimating it is 30-40% more transmissible than BA.5. This heightened transmissibility is likely driving the swell of post-holiday infections sweeping across the country.
Areas with earlier surges in JN.1 cases saw new COVID-19 hospital admissions double over a two week period in December. New York City is currently averaging around 3,500 new cases per day, up from under 700 per day in early November [3]. Hospitalization levels are rising as well, straining healthcare capacity [4].
| Date | % of U.S. COVID Cases Caused by JN.1 |
|---|---|
| December 3, 2022 | 2.9% |
| December 17, 2022 | 7.7% |
| December 24, 2022 | 39.5% |
Table 1: The rapid growth of JN.1 variant cases in December 2022 [5].
This swell of JN.1 cases does appear to be causing less severe outcomes on average so far. Early real-world data indicates about a 30-40% reduction in hospitalizations compared to earlier Omicron subvariants [6]. However, the sheer number of infections may still overload healthcare systems, and more data is needed to firmly characterize clinical severity.
Monitoring for New Symptoms
With new variants can come shifts in COVID-19 symptoms, making awareness and monitoring important. Some early physician reports suggest JN.1 may be more likely to infect lung tissue than earlier Omicron subvariants, potentially increasing pneumonia risk [7].
Headache and fatigue appear to remain the most common early symptoms. However, physicians are also noting reports of:
- Fever
- Body aches
- Cough
- Night sweats
- Brain fog
Monitoring for symptoms – including both typical and newly reported ones – remains essential for prompt testing and treatment if infected. [8]
Renewed Mitigation Measures
The swell of post-holiday COVID-19 infections has prompted renewed calls for masking and social distancing to blunt further spread. Los Angeles county has already reinstated an indoor mask mandate through late January [9]. Other counties may follow suit if hospital strains worsen.
Officials continue to strongly recommend getting updated COVID-19 booster shots, which provide protection against newer variants like JN.1. Moderna’s updated bivalent booster – targeting both the original Wuhan strain and currently circulating Omicron subvariants – was recently authorized for children as young as 6 months old [10]. Ensuring up-to-date vaccination status remains the best way to prevent severe COVID-19 illness.
What to Expect Next
Experts say the spread of highly transmissible new variants like JN.1 is not unexpected, but does highlight the need to continue genetic surveillance efforts [11]. It remains unclear whether JN.1 will overtake other Omicron siblings globally as well.
In the U.S., JN.1 cases are expected to continue rising through January based on early growth rates [12]. Some project the variant could cause up to 70% of new COVID-19 cases by the end of January 2023 [13]. Surges appear to be more pronounced in some regions, like the Northeast, compared to others so far.
Ultimately, epidemiologists say it remains difficult to predict how high case counts may rise or how much pressure hospitals may face in coming weeks. Redoubling mitigation measures can help flatten infection curves and ease strains on healthcare systems. Continued genomic surveillance, tracking of symptoms and outcomes, prompt data sharing globally, and access to updated vaccines will remain essential tools for staying ahead future viral mutations as the COVID-19 pandemic transitions towards endemicity over 2023.
To err is human, but AI does it too. Whilst factual data is used in the production of these articles, the content is written entirely by AI. Double check any facts you intend to rely on with another source.
