The total mass of all the SARS-CoV-2 in the world right now is between 100 g and 10 kg, according to an estimate by Ron Milo of the Weizmann Institute of Science and colleagues (Proc. Natl. Acad. Sci. U.S.A. 2021, DOI: 10.1073/pnas.2024815118). The work uses the typical viral load in various tissues and bodily fluids to estimate that an individual carries 1 billion–100 billion viral particles totaling a mass of 1–100 μg during peak infection. The team multiplies that number by the global caseload to determine the global mass. Carrying its analysis further, the group notes that inside each infected person, SARS-CoV-2 virions enter cells and replicate three to seven times, and each replication can introduce mutations. While not all these mutations will produce variants of concern, given the mutation rate, the number of viral particles involved, and the genome’s 30,000-nucleotide length, every possible nucleotide substitution is produced during a single infection, the researchers say. Worldwide, every mutation possible is generated and transferred to a new host every day.