KP.3 Variant Becomes Dominant Strain in U.S. as COVID-19 Cases Rise

The new KP.3 variant now accounts for 1 in 4 new COVID-19 cases across the United States, according to estimates from the Centers for Disease Control and Prevention (CDC) on Friday, making it the dominant strain nationwide.

KP.3’s rise coincides with increasing key metrics of viral spread. The CDC’s data shows virus levels starting to accelerate in the West through wastewater surveillance. Additionally, emergency room visits for COVID-19 have increased for all age groups in recent weeks, with infections likely growing in 30 states and territories, According to CBS News

Similarities and Differences with Other Variants

KP.3 is outpacing the KP.2 variant, which currently accounts for 22.5% of cases. Both KP.3 and KP.2 are similar to the JN.1 variant that dominated the previous winter wave. Natalie Thornburg, chief lab official at the CDC’s Coronavirus and Other Respiratory Viruses Division, noted that KP.2 and KP.3 are “nearly identical to each other with really one difference between the two of them.”

This difference is minor compared to past jumps in the virus, such as the emergence of the highly mutated BA.2.86 variant last year. However, early data suggests that KP.3’s mutations might better evade immunity compared to KP.2.

Vaccine Updates and Future Strains

As KP.3 becomes more prevalent, the FDA announced it would update this fall’s COVID-19 vaccines to target the JN.1 variant, turning down a newer formula aimed at KP.2. This decision came after the FDA’s Peter Marks highlighted the need to balance vaccine updates with the rapidly evolving virus, as per reports by TODAY.

Moderna’s data from animal studies indicated that its KP.2-targeted shot offered similar protection against the latest variants as a shot designed for JN.1. Pfizer’s KP.2 shot triggered better antibody responses for JN.1 variants, including KP.3. However, the FDA’s advisers were concerned that a KP.2-focused vaccine might not provide broader immunity for future strains compared to JN.1.

The CDC and FDA continue to monitor the situation closely, aiming to provide the most effective vaccine strategy against evolving COVID-19 variants.