[hashimotonomora]

At that low virion count it’s more about the probability that a virion will attach to the correct CD4 receptor and be able to work inside the cell. It’s not about the host's immune system defeating or being defeated on a number basis.

[est31]

To add to this, how many virions are needed for a successful replication to start depends on the virus.

https://www.virology.ws/2011/01/21/are-all-virus-particles-i...