Abstract
Quantitatively describing the time course of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection within an infected individual is important for understanding the current global pandemic and possible ways to combat it. Here we integrate the best current knowledge about the typical viral load of SARS-CoV-2 in bodily fluids and host tissues to estimate the total number and mass of SARS-CoV-2 virions in an infected person. We estimate that each infected person carries 109 to 1011 virions during peak infection, with a total mass in the range of 1 μg to 100 μg, which curiously implies that all SARS-CoV-2 virions currently circulating within human hosts have a collective mass of only 0.1 kg to 10 kg. We combine our estimates with the available literature on host immune response and viral mutation rates to demonstrate how antibodies markedly outnumber the spike proteins, and the genetic diversity of virions in an infected host covers all possible single nucleotide substitutions.
Highlights
Describing the time course of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection within an infected individual is important for understanding the current global pandemic and possible ways to combat it
We refer to TCID50 and plaque-forming units (PFU) more generally as “infectious units.”. As these two measurement modalities (RNA genome copies and infectious units) differ in reported values and interpretation—one method measuring the number of RNAs, the other measuring the number of infectious units—we report and compare estimates stemming from both approaches
Our quantitative analysis establishes estimates for the absolute number of virions present in an infected individual, as well as the number of virions produced during the infection and the total number of infected cells in the body
Summary
Our quantitative analysis establishes estimates for the absolute number of virions present in an infected individual, as well as the number of virions produced during the infection and the total number of infected cells in the body. It is important to note that viral load in different tissues in the host body changes throughout the infection, with some tissues likely infected early on and others later in the infection [53] Another way in which we can use our estimates to produce insights is by taking a global view and extrapolating from the numbers observed in a single infected individual to the entire population. The arithmetic mean of the number of particles produced over the course of infection of an average individual is 1012 to 3 × 1013 viral particles (Nviral particles produced per person), or 108 to 3 × 109 infectious units (see SI Appendix for the detailed derivation of the uncertainty range) One can contextualize these estimates using an absolute mass perspective.
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