The study by Clementi, who is director of the microbiology and virology laboratory of San Raffaele, compared virus samples from COVID-19 patients at the Milan-based hospital in March with samples from patients with the disease in May.  "The result was unambiguous: an extremely significant difference between the viral load of patients admitted in March compared to" those admitted last month, Zangrillo said.  Oscar MacLean, an expert at the University of Glasgow's Centre for Virus Research, said suggestions that the virus was weakening were "not supported by anything in the scientific literature and also seem fairly implausible on genetic grounds."