KP.2 and KP.3 Variants

The KP.2 and KP.3 variants are recent sub-lineages of the SARS-CoV-2 virus, which causes COVID-19. Both belong to the broader Omicron family, specifically evolving from the JN.1 lineage. They have gained attention in global health discussions because of their enhanced transmissibility and their capacity to evade immunity from earlier infections or vaccinations.

Background

The ongoing mutation of SARS-CoV-2 has led to numerous sub-lineages since its emergence in 2019. The Omicron variant, which became dominant worldwide from late 2021, continues to produce new sub-variants. Among these, KP.2 and KP.3 emerged in late 2023 and early 2024, respectively, and are part of a group of variants sometimes informally called “FLiRT” variants — a reference to characteristic spike-protein mutations that aid immune evasion. These mutations alter the virus’s surface spike protein, which determines how it binds to and enters human cells.
Both KP.2 and KP.3 descended from the JN.1 lineage and share many of its core genetic traits. However, they contain additional mutations that distinguish them from their parent strain and may slightly alter the virus’s behaviour, including its ability to spread or bypass antibodies developed through vaccination or prior infection.

Genetic and Virological Features

KP.2

KP.2 is defined by spike-protein mutations such as F456L, R346T, and V1104L, which modify parts of the virus that interact with human cell receptors and immune system antibodies. These changes appear to increase the variant’s viral fitness, meaning it can replicate and transmit more efficiently than some preceding variants.
Laboratory analyses indicate that KP.2 demonstrates an increased ability to evade neutralising antibodies, which may reduce the effectiveness of existing immunity. Despite this, KP.2 does not appear to cause more severe disease. Its main distinguishing feature is improved transmission potential rather than enhanced pathogenicity.

KP.3

KP.3 emerged soon after KP.2 and contains all of its predecessor’s key mutations, with additional genetic alterations such as Q493E in the spike protein and a deletion at S31. These confer a modest increase in immune evasion and possibly transmissibility. KP.3 has since become more prevalent than KP.2 in several regions, largely due to this evolutionary advantage.
Although KP.3 is slightly more immune-evasive, the difference between the two variants is relatively small. Both retain the Omicron family’s general features: high transmissibility and mild to moderate disease severity compared to pre-Omicron variants.

Spread and Prevalence

KP.2 was first detected in India in December 2023 and subsequently spread to multiple countries in early 2024. It became one of the leading causes of COVID-19 infections in parts of Asia and North America during the first half of 2024. KP.3 followed soon after and by mid-2024 had overtaken KP.2 in prevalence in several regions, including the United States and parts of Europe.
Both KP.2 and KP.3 are currently classified by the World Health Organisation as Variants Under Monitoring (VUMs), meaning they are not considered Variants of Concern but are tracked for potential public-health implications. Their spread demonstrates that SARS-CoV-2 continues to evolve even in populations with widespread immunity.

Clinical Implications and Immune Evasion

Early evidence suggests that neither KP.2 nor KP.3 causes more severe symptoms than previous Omicron sub-variants. The primary concern with these lineages lies in immune escape — their reduced susceptibility to antibodies induced by vaccination or prior infection.
Neutralisation studies have shown lower antibody titres against KP.2 and KP.3, indicating that existing immunity provides less protection from infection, though it still significantly reduces the risk of severe illness, hospitalisation, and death. Booster vaccinations remain effective at improving protection, and vaccine manufacturers have begun considering KP.2-based formulations for updated vaccine doses.

Virological Advantages and Limitations

Advantages (for the virus):

• Enhanced transmissibility due to improved viral binding and replication.
• Increased ability to infect individuals with prior immunity, leading to broader spread.
• Slightly improved survival against neutralising antibodies.

Limitations (for the virus):

• Some mutations may slightly reduce the virus’s binding efficiency or replication in certain cell types.
• High levels of global immunity and vaccination limit the variants’ capacity to cause large surges in severe cases.

Significance and Public-Health Relevance

The emergence of KP.2 and KP.3 illustrates the continuing adaptability of SARS-CoV-2 in response to global immunity pressures. Their ability to spread efficiently among populations with widespread prior exposure underscores the virus’s ongoing evolution and the necessity of constant genomic surveillance.
From a public-health standpoint, these variants highlight the importance of:

• Ongoing vaccine updates to match circulating strains.
• Continuous genomic sequencing and wastewater monitoring to detect emerging variants early.
• Reinforcing booster vaccination campaigns to maintain population-level immunity.

While KP.2 and KP.3 have not led to a significant rise in severe disease, they remind researchers and policymakers that the virus remains dynamic. The subtle genetic differences between these sub-lineages reinforce how small mutations can meaningfully alter transmission patterns and immune resistance.

Comparative Overview

Context and Broader Implications

In the broader context of viral evolution, KP.2 and KP.3 represent a gradual evolutionary drift rather than a dramatic leap. Their emergence supports the theory that SARS-CoV-2 is stabilising into an endemic pattern, with mutations mainly fine-tuning its transmissibility and immune evasion rather than altering its fundamental virulence.