"the times," quote, it seems like it's just a short time and people are already having to get boosters and the fact that they didn't realize that earlier in the rollout, shows me that there could be other questions that there could be out there. does this match the conversations that you and your colleagues are having with patients, doctor? >> i think from the beginning, we knew this was a new disease. we have a vaccine that's highly effective, but as you know, viruses can mutate. and as new strains of viruss have appeared, we are understanding better how effective are the vaccines for these new variants. for example, the delta variant. we also know from other vaccines like hepatitis and other conditions or even the flu vaccine that immunocompromised patients sometimes do not respond the same way to the same doss as other people. same thing for elderly people with the flu vaccine. this is not unique to covid. we're learning more about this disease in a short period of time. and for immunocompromised patients, we have robust studies