Professor Karina Butler:

I am happy to speak about the duration of immunity. The Deputy asked whether we had left out anything. If I gave the committee something today, I would probably have left something out by tomorrow because the data are evolving quickly. The answer is "Yes".

There are conflicting data. What we know is that antibody levels can decline over time, but we do not know how important which antibody level is in terms of protection from infection and whether the decline means everything in terms of protection. Our immune system consists not just of those antibodies but also our cellular immune system. The data coming out show that the immunity induced in the cellular immune system is much more long lived than that measured through antibodies. The whole story is not out yet by any means.