Peer review tells me that it's significantly less likely the researchers made mistakes handling the data, analyzing it, controlling for external causes, etc. A

Peer review tells me that it's significantly less likely the researchers made mistakes handling the data, analyzing it, controlling for external causes, etc. A peer-reviewed version also may change the wording of the abstract. The vaccine may be less effective on the South African variant than it is on the common strain, but if it's down to 85% from 95% we'll still do fine once a majority of people are immunized.