be harder to convince people to get because they are, by definition, one and done people? >> so the good news is that even a single dose induces immunological memory cells that are responsible for protecting against serious illness. we always talk about neutralizing antibodies. neutralizing antibodies fade over time but memory cells don't. for a long period of time -- the interesting thing about the j&j versus pfizer and moderna is really just a single dose of the j&j was able to induce excellent immunological. so that was the advantage of the j&j vaccine. hopefully people will get the second dose. even if they don't, they are pretty well protected against serious illness from the second dose. >> also this debate about mix and match. if you got a pfizer, whether you can get the boost for moderna. do you expect to vote on that issue, mix and match, any time soon?