Brazil’s public health institute Fundação Oswaldo Cruz (Fiocruz) has confirmed that the XFG strain of SARS-CoV-2 is circulating in Rio de Janeiro. Genome sequencing conducted with the city’s health department found the variant in 46 of the 74 samples collected between 1 and 8 July, giving the lineage a 62 % share of recent infections and making it the predominant strain in the capital. All reported cases were mild and none required hospitalisation, according to Fiocruz. Preliminary laboratory analysis indicates the variant carries mutations that slightly reduce antibody neutralisation, but researchers have seen no signs of increased clinical severity or significant loss of vaccine protection. On 25 June the World Health Organization placed XFG on its list of “variants under monitoring.” Rio is the fourth Brazilian state to detect XFG, following São Paulo (two cases), Ceará (six) and Santa Catarina (three). Fiocruz and local authorities said the finding underscores the need to maintain genomic surveillance and encourage residents to keep their Covid-19 vaccinations up to date alongside routine preventive measures.