Your doubt may not be warranted, as this passage shows:
Genetic bottlenecks are likely to occur quite frequently with RNA‐based respiratory viruses since respiratory droplets often contain only one to two infectious particles per droplet.7Modeling suggests that such bottlenecks likely drive down the virulence of a pathogen due to stochastic loss of the most virulent phenotypes
The whole article here:
https://onlinelibrary.wiley.com/doi/full/10.1002/jmv.26067