All squares are rectangles, but not all rectangles are squares. And parallelograms are kinda rectangles, but not. Think of a door when you're building a house. A one-degree shift in the angles on the door might still fit the frame. A ten degree shift won't at all. Seems small, but it's functionally massive.

Dead on. Since I know a lot of people who don't speak Science come here to learn, let me phrase it for them, too:

It likely has some effect, but specifically it is not targeted to the H5N1 influenza A virus.

The way vaccines work is by teaching your immune cells to target specific proteins on a virus (viruses are made up of many, many proteins, just like you and me). Now, different proteins have different shapes, so it's important for the vaccine to have the right counter-shape. Think of puzzle pieces. Anyway, if there's enough similarity in the proteins between HxNz and HyNw, then yeah, it'll do something, but it won't be perfect. Otherwise it'll do nothing at all.

Because they are all kinda similar, it probably does something, but not enough to really help. Part of the problem is that if you don't kill enough mean little microbes, it just doesn't matter. Going to Australia and shooting fifteen rabbits is not going to reduce the need for a rabbit-proof fence, right? So you gotta do better or you should've just stayed home.