Efficacy: 62-90%, depending on dose
Dose: 2 doses, 4 weeks apart
Storage: Stable in refrigerator for at least 6 months
Authorized so far in Britain, India and several other countries, this shot is cheap and easily stored, raising hopes that it could protect most of the world. Many scientists were puzzled, however, by data showing that its efficacy may depend on the strength of the initial dose or the gap between doses.