Last week, the Germans Trias hospital in Badalona detected its first two cases of covid caused by the new FLiRT variant, which has a greater contagion capacity than previous variants and is on its way to becoming dominant on a global scale.
The experience of the US, where FLiRT has been circulating for three months, indicates that the new variant will hardly cause a large increase in serious cases and hospitalizations.
Cases of the FLiRT variant have also begun to be detected at the Vall d’Hebron hospital, as well as in wastewater from Besòs, Igualada and Lleida, reports Andrés Antón, head of the Vall d’Hebron respiratory virus unit.
“This variant will spread and will tend to replace the current ones, but it is too early to know what impact it will have on infections and hospitalizations,” declares Roger Paredes, head of the infectious diseases service at the Germans Trias hospital. “It is possible, although not certain, that we will have a significant increase in infections in the coming weeks. If infections increase, hospitalizations will also increase among people most at risk of suffering complications from covid.”
In reality, FLiRT is not a single variant, but a set of variants that are first cousins ??to each other. They all derive from the JN.1 variant, which has been dominant in the world since last fall, and have independently acquired two mutations that increase their immune evasion capacity.
Specifically, they have replaced two amino acids of the S protein of the virus, which is the protein that antibodies recognize to neutralize it. They have replaced an F (symbol for the amino acid phenylalanine) with an L (leucine) and an R (symbol for arginine) with a T (threonine). Hence the name FLiRT.
Some versions of FLiRT also have an additional mutation that increases its ability to bind to and infect human cells. These variants (such as the one called KP.2) have a contagion capacity more than double that of the currently dominant JN.1, according to data published by virologist Benjamin Murrell, from the Karolinska Institute in Stockholm.
Data from the US confirm this greater contagion capacity. In mid-March, the KP.2 variant only represented 1.4% of all infections in the US and by early May it had already risen to 28% and had surpassed JN.1 as the dominant variant, according to data from the Center of Disease Control and Prevention (CDC). In the second half of May it is expected to exceed 50%.
But nothing indicates for now that the infections are more serious. “As far as symptoms go, we are not seeing anything new or different with these new variants; “We continue to see a lot of mild disease,” states virologist Andy Pekosz in an article published May 13 by Johns Hopkins University in Baltimore.
In Spain, the latest weekly report from the Acute Respiratory Infection Surveillance System (SiVIRA) indicates that the incidence of covid is increasing. In primary care, 24.3 cases per 100,000 inhabitants were registered in the week of May 6 to 12, the last with published data, which almost triples the 8.9 of the previous week.
In hospitals, the number of patients admitted with covid has increased by 57% in a week. But the SiVIRA data does not distinguish the FLiRT variants from the previous ones, so it is not possible to know if the increases are due to the arrival of these new, more transmissible variants of the coronavirus.
Population immunity against FLiRT infections is considered low in people who received their last vaccine dose or were last infected many months ago, reports Roger Paredes, from the Germans Trias hospital. On the contrary, immunity against serious complications of covid continues to be high.
The difference is explained because immunity against infections is mediated by antibodies that reduce over the months, while immunity against serious complications is mediated by immune cells that are maintained in the long term.
“The new variants are subject to surveillance; It seems that they could be more transmissible and that clinically they are not associated with a disease other than the one we have been seeing in recent months,” summarizes Antoni Trilla, epidemiologist at the Hospital Clínic in Barcelona. “Infections and cases of Covid could increase, but with the usual mild pattern now in the healthy population. We must be vigilant, especially with regard to the highest risk groups.”
