LB.1: The Latest COVID-19 Subvariant Circulating in the United States

A new subvariant, LB.1, has emerged as the third-leading COVID-19 variant in the United States, trailing closely behind the dominant KP.3 and KP.2. As of June 22, KP.3 accounts for an estimated 33% of cases in the U.S., followed by KP.2 at about 21% and LB.1 driving 17.5% of cases. Since the end of May, the share of cases caused by LB.1 has more than doubled, raising concerns about a potential summer surge.

Is There a Summer Surge?

In recent weeks, COVID-19 cases have been on the rise in most U.S. states, particularly in the West. According to the CDC, COVID-19 cases are growing or likely growing in 44 states, stable or uncertain in 5 states, and declining in one state, Hawaii. While the country is not currently experiencing a major nationwide surge in cases, the CDC estimates a steady increase in some regions with a test positivity rate of 8% as of June 22, indicating a rise since the previous week. As the summer vacation travel peaks and people gather indoors to escape heat waves, experts anticipate a continued rise in COVID-19 cases, especially following July Fourth travel.

Understanding LB.1

LB.1, part of the omicron family, is closely related to the FLiRT variants but has unique mutations in different parts of the spike protein. These mutations affect LB.1's ability to evade immunity, contributing to its high transmissibility. Although it is too soon to definitively compare LB.1 to other strains, there is no current evidence suggesting it is more transmissible than the FLiRT variants. The emergence of LB.1 continues the ongoing trend of the SARS-CoV-2 virus mutating and giving rise to new variants.

Symptoms and Severity

LB.1 does not appear to cause distinct or new symptoms and does not indicate a higher severity of the disease. Symptoms are similar to those caused by the FLiRT variants, ranging from sore throat, cough, and fatigue to loss of taste or smell, with generally milder infections observed. However, it is essential to note that individuals in high-risk groups, such as older adults and those with underlying health conditions, may still experience severe symptoms requiring hospitalization.

Vaccine Protection and Guidelines

Current vaccines offer protection against severe disease caused by LB.1 and other recent strains. The CDC recommends that high-risk groups receive an additional dose, and an updated 2024–2025 vaccine is expected to provide further protection. Testing remains crucial in identifying and preventing the spread of the virus, with guidelines emphasizing staying home while sick and avoiding contact with others upon testing positive. Individuals are encouraged to consider additional protective measures, such as wearing masks in crowded indoor spaces, practicing good hand hygiene, and improving ventilation.