Anthony Fauci Identify Quotations

The difference between H7N9 and H5N1, is that H5N1 kills chickens very rapidly, so it is easy to identify where the infected flocks of chickens are. H7N9 doesn't make the chicken sick, so it has been difficult to pinpoint where the infected chickens are.

If we could identify what that factor is -- and there's no guarantee we will, but if we can -- then one could direct your vaccine to elicit a response of that particular factor that is protecting them.