COVID-19 'FLiRT' subvariants on the rise across the US. Here's what to know

U.S. health officials are keeping an eye on the so-called "FLiRT" COVID-19 subvariants as the U.K. sees a rise in COVID hospitalizations.

"Our vigilance should increase as we see cases rise, primarily driven by increased travel and social gatherings typical of the summer months," said Dr. John Brownstein, an epidemiologist at Boston Children's Hospital.

Here's what to know.

What is the so-called FLiRT variant?

The FLiRT family, including KP.2 and JN.1, are strains of the Omicron subvariant. JN.1 has been the dominate COVID-19 strain as of late December of 2023.

The FLiRT subvariants generally cause milder illness compared to earlier strains such as Delta.

MORE | COVID JN.1 variant now leading cause of infections in US - Here's what you need to know

The Omicron coronavirus subvariant JN.1 now makes up 44.2% of COVID cases in the United States, according to the CDC.

What are symptoms of FLiRT variants?

Common symptoms of the emerging variant include sore throat, congestion, fatigue, and other mild symptoms similar to the common cold.

In more moderate and severe cases, fever and associated symptoms are possible.

Is it typical for COVID cases to rise over the summer?

Medical experts expected a rise in COVID-19 cases after weekly COVID hospitalizations in May hit their lowest level ever reported since the pandemic began, according to data from the Centers for Disease Control.

"While this uptick aligns with expected seasonal trends, we continue to monitor new variants closely to ensure our public health response remains effective and adaptive," Dr. Brownstein said.

Experts are now recommending that anyone who hasn't gotten last fall's vaccine to consider getting it now.

How can you tell if you have COVID or a cold?

PCR or rapid antigen tests are the most reliable way to distinguish between COVID-19 and other illnesses, according to the CDC. It is not possible to tell from your symptoms if you have cold, allergies or COVID without testing.

"Make sure to monitor for any symptoms and get tested promptly to prevent spreading the virus," Dr. Brownstein said.

Are current vaccines effective in combating the dominant COVID variant?

The latest available vaccines, including the updated booster targeting the XBB.1.5 subvariant, remain effective in preventing severe illness and hospitalization,

The formula of newer vaccines will be designed to protect against these FLiRT variants and are expected to be available this Fall.

"It's important to stay up to date with your vaccinations to maintain protection against current variants," Dr. Brownstein said.

The ABC News medical unit contributed to this report.