Screenshot/Twitter/CBS

Former Food and Drug Administration Commissioner Scott Gottlieb told CBS News' Margaret Brennan on Sunday that there needs to be a "plan B" in areas where the COVID-19 vaccine developed by the University of Oxford and AstraZeneca is widely used.

The Oxford-AstraZeneca vaccine has been shown to be quite effective in trials, but early findings suggest a drop in its ability to protect against the so-called South African variant. That's troubling because the vaccine is widely seen as a game-changer due to its lower-cost and easy storage method, making it the most likely to candidate to reach harder-to-access communities around the world, especially in developing nations. If the South African variant eventually becomes the dominant source of infections in those areas, that could put things back at square one.

The problem is, Gottlieb explained, the most logical replacement shot — the Johnson & Johnson candidate (which isn't on the market yet) — may be rendered ineffective in people who have already taken the Oxford vaccine since both rely on adenoviruses to draw an immune response. Gottlieb clarified that the latter point is not proven, but the risk is there until data becomes clear. In that case, he said the answer may be to turn to the vaccines that use mRNA technology, such as those developed by Pfizer and Moderna, instead, but they present significant distribution challenges. Tim O'Donnell