New SARS-CoV-2 Variant Fastest Growing Strain in US: CDC

The World Health Organization has characterized JN.1 as a variant of interest.

A new variant of SARS CoV-2 is reported to be spreading quickly across the United States and is currently the country's fastest growing strain, according to the Centers for Disease Control and Prevention (CDC).1

JN.1 is closely related to the BA.2.86 variant that the CDC has been watching since August with just a single change between the 2 strains in the spike protein. Originally detected in the US in September, JN.1 made up less than 0.1% of SARS-CoV-2 viruses by the end of October; the "best estimate" from the CDC currently is that JN.1 is responsible for approximately 1 in 5 new infections in the US.1

JN.1 is likely more transmissible than previous COVID-19 variants or is better able to evade the immune response, a primary reason for the continued spread, according to the CDC.1 Jay Weiland, a COVID modeler, told Axios on Monday that the new strain would dominate other circulating variants "within a week, and that estimated new infections at approximately 965 000 per day "aren't close to peaking."2

On Tuesday, the World Health Organization (WHO) classified JN.1 a variant of interest based on rapid increase in the global proportion of sequences available from 3.3% in early November to 27.1% in early December.3 The WHO also stated that despite the velocity of the variant's ascent to dominance in some countries, there have been no reports of elevated disease severity associated with it. "JN.1 does not suggest additional public health risks relative to the other circulating Omicron descendent lineages."3

The CDC concurs with the WHO assessment and both organizations state that current COVID-19 vaccines continue to protect against severe disease from JN.1.1,3 "Despite this, with the onset of winter in the Northern Hemisphere, JN.1 could increase the burden of respiratory infections in many countries," the WHO said in a statement.3

The US could be at risk for such an increase as the incidence of seasonal respiratory viruses continues to rise quickly. In a December 14 Health Advisory the CDC warned health care professionals that in the past 4 weeks, hospitalizations across age groups for influenza and RSV rose 200% and 60%, respectively, while pediatric emergency department visits for pneumonia have been rising since September. COVID-19 hospitalizations rose 51% during the 4-week period.4

To mitigate the risk of taxing a health care system already frayed by COVID-19 pandemic sequelae, both WHO and CDC recommend continuing standard COVID-19 prevention and mitigation strategies including staying up to date with vaccination, also a point of weakness in the US, according to the CDC. In its alert to clinicians, the organization said vaccination coverage remains low this season across all age groups relative to the same time last year and for all 3 of the cocirculating respiratory viruses, prompting the call for health care professionals to "leverage all available tools to increase immunization."4

Masking in crowded areas, vigilant handwashing practice, and staying at home if sick continue to be endorsed by all public health agencies.

References
1. Update on SARS-CoV-2 variant JN.1 being tracked by CDC. CDC respiratory virus updates. CDC. December 8, 2023. Accessed December 20, 2023. https://www.cdc.gov/respiratory-viruses/whats-new/SARS-CoV-2-variant-JN.1.html
2. Bettelheim A. New COVID strain rises in U.S. ahead of holidays. Axios. December 20, 2023. Accessed December 20, 2023.
3 World Health Organization. Accessed December 19, 2023. https://www.who.int/docs/default-source/coronaviruse/18122023_jn.1_ire_clean.pdf?sfvrsn=6103754a_3
4. Halsey G. CDC: "Leverage all available tools" to Increase Flu, RSV, COVID vaccination. Patient Care Online. December 19, 2023. https://www.patientcareonline.com/view/cdc-leverage-all-available-tools-to-increase-flu-rsv-covid-vaccination