Absolutely, the US should conduct such research and keep it secret!
Bio and chemical weapons are strategic weapons. That is, they can wipe out governments, armies, cities, states, countries … They are also cheap strategic weapons, sometimes called a poor mans nuclear weapon. But in my mind, they are more devastating than a nuclear weapon, certainly I feel that their impact can be felt much further from the release zone.
History has shown us that nation states aren’t the only people with access to such weapons (Sarin in Japan). Terrorists also have access to such weapons, and far more will to use them.
In order to create vaccines, they need to fiddle with viruses. I am sure that they are taking every precaution, including full isolation of hot zones.
I think that all US citizens (and can you give the technology to Australia as well?) would sleep safer knowing that their government has detectors for such weapons and a vaccine, should it ever be released. However, I wouldn’t count on the fact that the vaccine would definitely work. These days recombinant DNA and genetic manipulation have ways of tailoring each virus so that a vaccine for one strain would not work on another.
I doubt that we would have to worry about the US using the viruses or chemicals at any time soon. If the bio and chemical warfare programmes were dismantled during the Nixon presidency, like they were declared to have been, then the only stock available would be quite small. However, the US would have the ability to be up and running again in no time, if it were necessary.
As for keeping it secret, I think that having enemies safely working away at something that the US already has a vaccine for is better than having them dump the entire programme and go looking at something entirely different. It suppose isn’t such a bad thing saying we have a biowarfare facility aimed at looking into vaccines and such. But don’t be giving the location of it away. I doubt that the first thing you want is to have the sh!t bombed out of the only facilities capable of detecting and neutralising the enemies weapon. But I would think that any information surrounding strategic weapons would be highly classified (now, lets not go into the stupidity of the US government and some of the stuff that they allowed to be publically accessible).
As for the NSA? What better cover than putting Noel on your building. But that whacking great big carpark is a dead giveaway 
Li