>> Hi, my name's Paul Offit.
I'm talking to you today from the Vaccine Education Center, Children's Hospital of Philadelphia.
I want to talk to you about something that happened at the Advisory Committee for Immunization
Practices meeting at the CDC on June 22nd of 2016.
At that meeting, the ACIP recommended that FluMist, the live attenuated influenza vaccine
that has been given to children for many years, not be given for the upcoming 2016–2017 season.
So why?
How did we get to this point?
Remember, a few years ago, FluMist was recommended
frankly as a preferred vaccine for children. It was recommended as preferred over
the inactivated influenza vaccine, which was given as a shot,
because FluMist appeared to work better, had a greater percentage efficacy than did the
inactivated vaccine.
That because the vaccine virus of FluMist reproduced itself at the nasal mucosal surface,
that it had the capacity to drift, if you will, and that it maybe would have thought
to have been better against strains where the match wasn't perfect between what was in the vaccine
and the strains that were circulating.
Also because it reproduced at the nasal mucosal surface, it induced the local immune response;
therefore, more likely that when one was exposed to wild type or natural virus, then you would
be less likely to transmit it from one person to the other, and more importantly I think,
most importantly, it's just easier to give and I think it's preferred by many children
to get the FluMist rather than to get the shot.
But over the last three years, FluMist has dramatically underperformed the inactivated vaccine.
In fact this most recent year, the 2015–2016 season, the percent efficacy was estimated
to be about 3%, which frankly is not better than placebo.
There ... it's unclear exactly what happen but, there is certainly reasons that have been proposed.
One is that when you give the inactivated vaccine, for example, into the muscle, you
know that you're giving, for example, 15 micrograms of hemagglutinin per strain in the muscle.
You know that each of the 15 micrograms of hemagglutinin per strain will be taken up
by local lymph nodes, processed, and presented to the immune system.
When you give FluMist, when you give the live attenuated vaccine, it's not 15 micrograms
of antigen or hemagglutinin per strain, it's much, much less than that because you depend
on that vaccine virus reproducing itself at the nasal mucosal surface and essentially amplifying
the amount of antigen that's originally in that vial.
So I think you can consume, that at some level, replication wasn't occurring at the nasal
mucosa surface in a manner that was effective enough to generate large quantities of antigen.
So why is that?
Why had it worked earlier but not later?
I think one reason and frankly one that makes the most sense to me is that when we went
from the trivalent of flu vaccine, FluMist, to quadrivalent flu vaccine, FluMist, we had
two B strains, and I think it's possible that one of the B strains may have outcompeted
the other three strains.
So that you have a better immune response to one of the B strains but not to the other
three strains.
And this has happened before.
I mean if you look actually at rotavirus vaccines, sometimes one of the strains will, for example,
with RotaTeq will reproduce itself better when you first get it.
But again, you give multiple doses.
So you have a chance then to have those other strains reproduce themselves better.
Same with the oral polio vaccine; the type 2 polio vaccine actually is contained — was
contained in the oral polio vaccine at a greater concentration than the other strains.
So I think you have to account for that when you give viruses, especially when it's more
than one virus and it needs to reproduce itself in order to evoke a good immune response.
It's hard to know whether this is the case. Certainly I think we can get answers to that
by doing shedding studies to see whether or not one of the strains is outcompeting, whether
we need to balance those strains differently.
I'm optimistic FluMist can come back into the United States, but only I think when we
know those answers.
Hopefully that's helpful.
Thank you.