Dr. Colm Henry:

The most prominent reason is that they were no longer effective against the circulating variants. While the shelf life is important for any vaccine and we have those in any set vaccination programmes, the other set vaccination programmes deal with steady-state viruses that behave in a relatively predictable way. With this one, as I said, we are still getting used to it. It is becoming more seasonal and we also know, of course, that the effectiveness of the vaccine begins to wear off after a number of months, which makes it different.