I’m not an expert on this, but my guess would be: it’s logistically very difficult to produce the required number of doses. They’ve been gearing up all over the

I’m not an expert on this, but my guess would be: it’s logistically very difficult to produce the required number of doses. They’ve been gearing up all over the world to get ready. So, I would think that you really don’t want to spend those resources on a vaccine that’s either 1) not safe, or 2) not as effective as you thought it was.