Perhaps this is a place to bring up particle to pfu ratio? The above is great for when talking about phage, for example, when the ratio approaches 1. But with something like polio when it can be very high (>1000 ??), then it’s not that all cells don’t receive “a particle” at MOI=1 – but that they don’t get an “infectious dose”. Not sure how to say it better – enough to initiate an infection.So why does polio require 1000 virions to make an infectious dose? I don’t buy the idea that most of the particles are not “viable”.
into the number of virus particles in the sample, we obtain a number known as the particle-to-PFU ratio. It is a measure of the fraction of virus particles in a given sample that can complete an infectious cycle. For many bacteriophages, the particle-to-PFU ratio approaches 1, which is the lowest value that can be obtained. A value of 1 means that every virus particle in the sample is able to form a plaque.