The new COVID variants spreading in the US are called ‘FLiRT.’ But why?

The "FLiRT" COVID-19 variants are a new group of strains circulating in the United States, which now account for over one in four cases nationwide.

Although cases and hospitalizations have been down across the country, the virus that causes COVID-19 continues to mutate and give rise to a seemingly endless stream of new variants.

The latest to gain attention, KP.2 and KP.1.1, are part of a new family of subvariants nicknamed "FLiRT," which were detected in wastewater samples earlier this spring and are now driving an increasing proportion of cases.

According to experts, KP.2 and KP.1.1 may be more transmissible and better at escaping prior immunity than previous variants, which has sparked concern about a possible summer wave.

The variants have also sparked plenty of reactions and jokes on social media. Are we "flirting" with dangerous new variant? Why is it called FLiRT in the first place?

What are the FLiRT COVID-19 variants?

KP.2 and KP.1.1 are both types of the omicron subvariant JN.1.11.1, which is a direct descendant of JN.1, the dominant strain for most of the winter, previously reported.

KP.2 and KP.1.1 are similar to JN.1, but they picked up additional mutations which appear to be giving the new strains an advantage over other variants, Dr. Albert Ko, infectious disease physician and professor of public health, epidemiology and medicine at Yale School of Public Health, previously told

Last month, KP.2 rapidly overtook JN.1, which drove a surge in COVID cases last winter, to become the dominant strain in the U.S. Currently, KP.2 accounts for over 25% of cases, according to the latest data from the U.S. Centers for Disease Control and Prevention.

"I think these two mutations together are making KP.2 a better virus in that it maintains its ability to transmit, but also now evades some of the pre-existing immunity in the population,” Andrew Pekosz, Ph.D., virologist at Johns Hopkins University, previously told

As KP.2 and KP.1.1 gained traction, scientists on social media came up with a catchy new nickname, “FLiRT," to use instead of the mouthful of letters and numbers.

It's distinct from other unofficial variant names — Pirola, Eris, Arcturus and Kraken — which seem to fall into a theme of Greek mythology and constellations.

The name "FLiRT" was first coined in March on “X,” formerly known as Twitter, by T. Ryan Gregory, Ph.D., a professor of evolutionary biology at the University of Guelph in Ontario. Gregory regularly posts about the evolution of SARS-CoV-2, the virus that causes COVID-19, and is behind many of the other popular variant nicknames.

“I think clear, accessible communication is important for getting across the fact that the virus is still widespread and evolving rapidly," Gregory tells

Why are they called FLiRT variants?

Not surprisingly, the new strains aren’t spread by winking, giving compliments or other signals of romantic interest and attraction. They have nothing to do with flirting at all.

The name “FLiRT” is based on the technical names for the variants' spike protein mutations or the specific amino acid changes, Gregory notes. These two mutations are at position 456 and position 346, Pekosz said.

“Each amino acid has its own letter abbreviation. FLiRT is F456L + R346T, or phenylalanine (F) to leucine (L) at position 456 and arginine (R) to threonine (T) at position 346,” says Gregory.

The "FL" and "RT" were combined into the nickname "FLiRT," according to the Infectious Disease Society of America.

When new variants emerge, they are described using a combination of letters and numbers, such as KP.2, JN.1 or HV.1. These letters and numbers refer to the variant’s “Pango lineage,” which is similar to a family tree, with lineages descending from the parental strain, according to the CDC.

A group of closely related viruses is called a lineage and the direct descendants of each variant are referred to as a sublineages — for example, BA.2.75 is a sublineage of BA.2. These lineages are named using an alphabetical prefix, such as BA or XBB, followed by a numerical suffix (such as .1 or .1.1.5), per the CDC.

Think of KP.2 and KP.1.1 as branches extending from the JN.1 branch, which is a direct descendent of BA.2.86 or Pirola.

As the virus continues to mutate and change, these technical names can become long and difficult to remember or say. That's where nicknames come in handy.

In 2021, the World Health Organization introduced a simpler system to label key variants. Each new variant of interest and variant of concern would be named after letters of the Greek alphabet. These include the alpha, beta, delta and omicron lineages.

Omicron (B.1.1.529) began circulating in the fall of 2021. Since then, the omicron virus variant has mutated and given rise to new subvariants. All of the COVID-19 strains that have emerged and gained dominance since 2022 have been descendants of omicron.

"Officially, everything since late 2021 has been nicknamed omicron. That now includes several thousand designated variants," says Gregory. These include omicron BA.2, BA.4 and XBB. Once again, the clunky combinations of letters and numbers are used to distinguish between key subvariants.

"A group of volunteer variant trackers began using our own informal nicknames two years ago, first based on mythological creatures (Kraken for XBB.1.5), and then based on astronomical entities (Pirola)," says Gregory.

Variant trackers had been discussing easier ways to describe the most important mutations showing up in JN.1’s descendants, says Gregory. “Things are evolving rapidly, so for now it makes more sense to focus on mutations of interest rather than individual variants,” Gregory adds.

Previously, in 2023, scientists came up with the nickname "FLip" for variants with another combination of mutations (L455F + F456L). Inspired by "FLip," Gregory suggested "FLiRT" for the latest strains.

Nicknames like FLiRT help make sense of the "variant soup," Gregory wrote in a tweet.

Despite its playful name, the new set of COVID-19 variants are nothing to joke about. It's important to take precautions against COVID-19 and keep up to date with vaccinations to prevent severe disease and complications.

"Mitigations like respirators, ventilation, air filtration and avoiding exposure are all variant-proof and will work against FLiRT," says Gregory.

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