The total number and mass of SARS-CoV-2 virions

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.

Keywords: COVID-19; genetic diversity; variants of concern; viral biomass; viral load.

Fig. 1.

A schematic representation of the estimate of the number of virions in an infected individual. The estimate is made using the viral load measured in a gram of rhesus macaque tissue (–10, 13) multiplied by the mass of human tissues in a reference adult person with a total body weight of 70 kg (11). In the digestive tract, the concentrations are close to the detection limit. We assume the number of virions is similar to the number of RNA copies.

Fig. 2.

Estimate of the number of infected cells and their fraction out of the potential relevant host cells.

Fig. 3.

The relationship between the number of virions produced in an infected individual and the evolution of SARS-CoV-2. We use our estimates for the total number of virions produced during an infection, along with other epidemiological and biochemical characteristics of SARS-CoV-2, to estimate the rate of mutation accumulation within an infected host (A) and within the population (B). We consider both the evolution along a specific genetic lineage of virions and the diversity among a population of virions—either within an infected host (A) or within the total population (B). In addition, we look at the de novo mutation generated and transmitted to the newly infected in comparison to all possible single base mutations (C).