Covid, Nimbus "more transmissible but less aggressive. The variant in Italy for 1 month already"

"Despite" the new Covid variant NB.1.8.1 or 'Nimbus' "showing greater transmissibility, the genomic data found classify it as less aggressive than recent ones . Furthermore, it should always be remembered that the vaccine, developed on the basis of the previous variant (JN.1), combined with the immune memory of past infections, should provide adequate protection. However, this does not mean that we can lower our guard or relax our vigilance regarding the study of new variants. The data presented reflect the current situation, but since the virus is continuously mutating, our only effective tool remains continuous and complete genomic surveillance". This is the conclusion of an Italian study signed by Francesco Branda (Campus Bio-Medico University of Rome), Massimo Ciccozzi (Campus Bio-Medico University of Rome) and Fabio Scarpa (University of Sassari), sent to the journal 'Infectious Diseases'.

The newcomer NB.1.8.1, "which was designated Vum (Variant under Monitoring) on ​​May 23 - the authors recall - does not represent a monophyletic group. It groups within a heterogeneous clade that also includes specimens of XDV, which is a particularly interesting aspect since NB.1.8.1 is actually a descendant of XDV, which in turn originates from JN.1, just like all the variants that have been circulating since the end of 2023. However, NB.1.8.1 does not yet appear to have differentiated sufficiently to form a distinct genetic cluster".

Currently, "the number of cases of NB.1.8.1 infection is increasing - the study highlights - As of May 18, 2025, NB.1.8.1 sequences had been reported in Gisaid from 22 countries, representing 10.7% of the sequences available globally until the end of April. However, considering that the current global case numbers are comparable to those observed in July 2024, the situation - the researchers underline - does not appear alarming. It is normal for the virus to continue to evolve, with a sort of replacement of variants that favors the newer ones that show greater transmissibility. In fact, at the beginning of 2025 XEC was the most widespread variant reported globally, closely followed by KP.3.1.1, the previous dominant variant. In February XEC began to decline, while LP.8.1 increased in prevalence. By mid-April, LP.8.1 showed a slight decline, coinciding with a number increasing number of NB.1.8.1 detections".

"We had already found the new Nimbus variant over 1 month ago in Pisa on a patient admitted to the emergency room. Unlike Genoa, also because the procedure requires 2 weeks, we isolated it and propagated it in the laboratory. It is indeed different from the others. It does not induce evident cellular damage, demonstrating how the virus is progressively attenuating and adapting to our cells", says Mauro Pistello, director of the Virology Unit of the University Hospital of Pisa.

Officially, the first case of the new Covid Nimbus variant (NB.1.8.1) in Italy was registered in Genoa, at the San Martino polyclinic hospital, in a 69-year-old 'fragile' patient with an oncohematological disease.