also more deaths. Other explanations: that in Mexico people have, in addition to swine flu, other viruses that make for a more deadly combination than swine flu alone. It's also possible that the virus infecting the rest of the world is a weaker version than the one in Mexico. Among the swine flu mysteries: Why only deaths in Mexico ? 11. Could this new swine flu virus have been manufactured by bioterrorists ? That's the theory on some conspiracy theoristsWeb sites. But experts do n't believe it. If you were a bioterrorist you 'd want to create something that's a lot more deadly than this, said Dr. Gerald Evans, an associate professor of microbiology at Queen's University in Canada. The problem with influenza is that the second you put it into people, it replicates and mutates very quickly. Even if you created the perfect bioweapon, within a few generations of transmissions, it would n't do what you planned for it to do. 12. I get a flu shot every fall. Will that help protect me against swine flu ? The short answer is that the CDC says it's very unlikely, Schaffner said. But he said it might be possible. I think it's a bit of an open question whether repeated flu shots over years would provide a measure of protection. 13. I was in Mexico two weeks ago. Could I have contracted swine flu, and the symptoms just have n't shown up yet ? No. The incubation period of the swine