Professor Philip Nolan:

It is a plausible scenario but it is simply not true. If I am due to take a flight in 72 hours' time, and the Deputy is absolutely right that I could pick up the virus in the next 72 hours, but if I am swabbed right now, go out that door and I am immediately exposed to the virus, and pick it up then it will take three to four days for that virus to replicate inside me before it is detectable by any test, and probably longer before it is detectable by a rapid antigen test. So the difficulty is that I will have taken my flight and arrived at my destination before I am in any way likely to be detectable. So this is why we have this caution around how frequently one tests and it depends on all kinds of things like prevalence. It has not been tested. There has not been a proper study done but I can say a rapid antigen definitively would not pick up an exposure that occurred after my swabbing. It may detect an exposure that occurred beforehand. It is quite unlikely, given the evidence that we have, that being swabbed for PCR up to 72 hours beforehand could be improved upon by adding an antigen test up to 48 hours before I board the flight.