In fact, in 2009, they nearly got there, when a large trial in Thailand showed an experimentalvaccine protected about one third of the people who received it from HIV infection.
Early results showed that, rather than preventing HIV or reducing the viral load in people who received it, the experimentalvaccine may have increased their chances of become infected.
Portuguese scientists said they had developed an experimentalvaccine against tooth decay which was successful in laboratory tests on rats and could pave the way for a version that works for humans.