Professor Martin Cormican:

In terms of the decisions that are made in different countries, I would just go back to the filter analogy. Some countries may have chosen to use a filter with a smaller pore size. We know that antigen testing will let more infectious people through than the PCR test. So some people make policy decisions about which filter they are going to use. We are using the higher grade filter and some countries may choose to use the lower grade filter. It is a question of which filter one chooses to use.