A multi-institutional study estimates that during peak infection with SARS-CoV-2 a person carries between 1 billion and 100 billion virions with a total mass of no more than 0.1 milligrams.

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The study published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS) suggests that the sum of all virions currently found in human hosts may amount to an estimated mass ranging between 100 grams and 10 kilograms. Additionally, the results suggest that the genetic diversity of virions in a single infected host likely covers all possible single nucleotide substitutions, according to the authors. The authors of the paper are: Ron Sender, Yinon M. Bar-On, Shmuel Gleizer, Biana Bernshtein, Avi Flamholz, Rob Phillips, and Ron Milo.

Quantitatively describing the time course of the SARS-CoV-2 infection within an infected individual is important for understanding the current global pandemic and possible ways to combat it. Here the researchers integrate the best current knowledge about the abundance of potential SARS-CoV-2 host cells and typical concentrations of virions in bodily fluids to estimate the total number and mass of SARS-CoV-2 virions in an infected person.

"We estimate that each infected person carries 10 9 -10¹¹ virions during peak infection, with a total mass of about 1 mg-0.1 mg, which curiously implies that all SARS-CoV-2 virions currently in the world have a mass of only 0.1-1 kg", researchers noted. Knowledge of the absolute number of virions in an infected individual can put into perspective parameters of the immune system response, minimal infectious doses and limits of detection in testing. The researchers also described the significance of the study by saying, "Knowing the absolute numbers of virions in an infection promotes better understanding of disease dynamics and response of the immune system".

Through the collaborative study, the researchers used current knowledge on the concentrations of virions in infected individuals to estimate the total number and mass of SARS-CoV-2 virions in an infected person. Although each infected person carries an estimated 1 billion to 100 billion virions during peak infection, their total mass is no more than 0.1 mg. "This curiously implies that all SARS-CoV-2 virions currently in all human hosts have a mass of between 100 g and 10 kg", researchers noted.