15% of the genetic material from 1918 flu virus was decoded, despite there is no living surviving virus. They analyzed the genetic material changes in old tissue sample of patients.
In 1918 science didn't even knew what was a virus, since eletronic microscopes didn't existed yet. They tried a vacine believing it was caused by a bacteria.
http://www.pbs.org/wgbh/americanexperie ... benberger/" target="_blank
The virus killed more young health people than older or childs. This is because the imune system response could be too strong and creates a problem reaction. Something like that happens with dengue fever (dandy fever breakbone fever) here on Brazil, since after the first infection, a new one can be more dangerous than the first, as it's 4 brands of similar virus and antibody memory leads to a stronger reaction in each new infection. So each time someone get dengue it's more dangerous.
A vacine against dengue was developed and it's in final stages of tests, but the vacine it's indicated for people who never got a version of dengue (4 versions can infect and people can 4 dengue up to 4 times), cause the vacine it's not 100% efficient and it can set the imune response in danger way in case a someone get real dengue.