FLiRT variants threaten summer Covid surge, but experts say risk remains uncertain

CNN
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Covid-19 levels are about the lowest they’ve ever been in the United States, but a new wave of virus variants once again threatens to disrupt the downward trend as the country heads into summer.

KP.2 – one of the so-called FLiRT variants – has overtaken JN.1 to become the dominant coronavirus variant in the United States, according to data from the US Centers for Disease Control and Prevention. Data through May 11 shows it is responsible for more than a quarter of the country’s cases, almost twice as many as JN.1. A related variant, KP.1.1, causes about 7% of cases, according to CDC data.

The FLiRT variants are offshoots of the JN.1 variant – all part of the Omicron family – which caused this winter’s surge. The acronym in the name refers to the locations of the amino acid mutations that the virus has detected – some in places that help it evade the body’s immune response and others that help it become more transmissible.

Covid-19 variants are “accumulated mutations that do one of two things: They either cause the antibodies you built up from vaccination or infection to no longer bind to the virus – we call this evasion of immunity — or they increase the strength “in which viruses bind to cells,” said Dr. Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health.

It’s become a familiar pattern in how the virus that causes Covid-19 continues to evolve, but experts say we still don’t know enough to predict exactly where changes will occur next or how they will affect how the virus travels. population.

Mutations in FLiRT variants make increased transmissibility – and a possible summer surge – a real threat. Covid-19 is settling into certain seasonal patterns, which included a summer bump in years past, but the exact level of risk for this year is unclear.

“We’ve had variants in the past that started out pretty strong and didn’t take over. These subvariants could gradually become dominant, or they could represent between 20 and 40% of cases and then stay there. We just have to see,” said Dr. William Schaffner, an infectious disease expert at Vanderbilt University. “The virus continues to be in charge. He’s going to tell us what he’s going to do. All our crystal balls are pretty cloudy.

Covid-19 surveillance has declined significantly since the public health emergency in the United States ended a year ago, also adding to uncertainty. But the available data is consistent. For now, wastewater monitoring suggests that virus activity is very low and decreasing in all parts of the country, and that Covid-19 hospitalization rates remain extremely low.

“We have learned from the labs that the FLiRT variants so far appear to be as transmissible as the other Omicron sub-variants, meaning they are indeed very contagious. But they don’t seem to produce more severe disease or any sort of distinctive disease from a clinical presenting symptom standpoint,” Schaffner said.

As of May 1, the requirement for all hospitals to report Covid-19 data to the federal government expired. But Vanderbilt University Medical Center in Schaffner is part of a surveillance network run by the CDC that continues to track trends based on a sample of hospitals covering about 10% of the U.S. population. Covid-19 hospitalization rates fell from nearly 8 new admissions per 100,000 people in the first week of the year to about 1 new admission per 100,000 people at the end of April, the data shows.

Even though the FLiRT variants pose some risk this summer, experts remain focused on what could happen in the fall.

“If I had to predict, I would say it could lead to a few more cases, a small increase this summer. But it will really be a question of which variant will be present in the fall,” Pekosz said. “The fall is probably when we should expect an increase in Covid cases. And if we have a variant there that has a lot of these immunity-evading mutations, then the potential for a larger surge in the fall is greater.

Fall and winter pose a greater risk because of the immunity that has built up within the population, he explained.

“The virus now needs better conditions to transmit, and those better conditions to transmit will likely occur in the fall when the weather cools, people spend more time indoors, and they are more likely to be found in environments where respiratory virus transmission occurs more effectively.”

A study published Wednesday in the medical journal JAMA recalls the burden that Covid-19 continues to weigh on the United States. This winter, even though Covid-19 hospitalization rates were much lower than in previous years, the virus remains more deadly than the flu. A study of thousands of hospitalized patients found that 5.7% of Covid-19 patients died, compared to 4.2% of those hospitalized with the flu. In other words, Covid-19 carried about a 35% higher risk of death than the flu.

People who received the last Covid-19 vaccine last fall may still have some protection against the latest variants; that vaccine targeted a different strain but was just as effective against JN.1, and experts say some of those benefits could extend to its FLiRT relatives. People who have had a recent infection – particularly since the beginning of the year, when JN.1 was predominant – may also have some protection. But immunity wanes over time.

In June, the U.S. Food and Drug Administration’s vaccine advisory committee will meet to discuss recommendations for which version of the Covid-19 vaccine will be available this fall. The meeting was postponed for about three weeks to “allow more time to obtain monitoring data” in order to have “more up-to-date information when discussing and making recommendations,” according to an article published on the federal agency’s website.

For now, experts say, the risk remains relatively low.

“As with all things Covid, our outlook could change in a week or two. But right now, we’re in a really good place – the best we’ve been in a long, long time,” Schaffner said.