Unveiling the FLiRT Family: Understanding the KP.1 and KP.2 COVID-19 Variants

Unveiling the FLiRT Family: Understanding the KP.1 and KP.2 COVID-19 Variants

The COVID-19 pandemic has continuously evolved, bringing new challenges as the virus mutates. Among the latest developments in the virus's evolution is the emergence of the FLiRT family of variants, particularly the KP.1 and KP.2 strains. These variants have raised questions about their infectiousness and the effectiveness of current vaccines.

What Are the KP.1 and KP.2 Strains?
The KP.1 and KP.2 strains belong to a subgroup of COVID-19 variants known as the FLiRT family. This group of variants is characterized by specific mutations in the spike protein of the virus, which is crucial for the virus's ability to enter human cells. The spike protein mutations can potentially affect how easily the virus spreads and how well it can evade the immune response.

KP.1 Variant
The KP.1 variant was first identified in early 2024 and has since been detected in several countries. Key mutations in KP.1 include changes in the receptor-binding domain (RBD) of the spike protein, which may alter the virus's ability to bind to human cells. Early studies suggest that KP.1 may have an increased transmission rate compared to previous variants, but more research is needed to confirm these findings.

KP.2 Variant
Closely related to KP.1, the KP.2 variant also features significant mutations in the spike protein. However, it has additional changes that might influence its behavior and interaction with the immune system. KP.2 has shown signs of rapid spread in regions where it has been detected, raising concerns among health authorities. Like KP.1, the full impact of KP.2 on transmission and severity is still under investigation.

Infectiousness of KP.1 and KP.2
Both KP.1 and KP.2 have mutations that suggest they could be more infectious than earlier strains of the virus. Increased transmissibility is often linked to mutations that enhance the virus's ability to bind to host cells or replicate more efficiently. Preliminary data indicate that these variants might spread more quickly within communities, potentially leading to higher case numbers.

Are current vaccines still effective?
Against JN.1, the current vaccines designed around Omicron XBB.1.5 do generate some cross-reactive antibodies, said Professor Pekosz.

Studies have not been done with some of the newer variants, he noted, adding that those are likely to be "a little less cross-reactive".

Dr Leong provided a similar view. 

“We know that the XBB1.5 vaccine was about 50 per cent effective against the JN.1. We suspect that the current vaccine will be less effective in preventing infections with KP.1 and KP.2,” he told CNA.

"The chief reason is the presence of the FLiRT mutations. The F amino acid became L and the R became a T. This allowed the virus to evade the existing immunity against COVID."

It has also been several months since many people received their last dose of the vaccine, and that immunity wanes over time.

Scientists say vaccination remains the best bet, especially against severe illness.

“We firmly believe that it (the vaccine) is still effective against preventing severe disease such as hospitalisation and death,” Dr Leong said.

Singapore's Health Ministry said that during the peak month of the previous JN.1 wave in December 2023, the incidence rate of COVID-19 hospitalisations and intensive care admissions among seniors aged 60 and above was 25 per cent higher in those who had not kept their vaccination updated compared to those who had.

The US CDC said the agency was continuing to monitor how vaccines perform against KP.2.

Governing bodies like the WHO and the US Food and Drug Administration are also expected to recommend a formulation for updated COVID-19 vaccines that will roll out in early fall.

New COVID-19 variants are likely to crop up after a decision is made, but Professor Pekosz said the goal remains to select a formulation that will match the circulating variants as closely as possible.