Explainer-How safe is it to switch and space COVID-19 vaccine doses?

FILE PHOTO: Brian Pinker, 82, receives the Oxford University/AstraZeneca COVID-19 vaccine from nurse Sam Foster at the Churchill Hospital in Oxford, Britain January 4, 2021. Steve Parsons/Pool via REUTERS

LONDON/CHICAGO (Reuters) - Britain and other nations are considering ways to stretch scarce supplies of COVID-19 vaccines, including by delaying second doses, reducing dose sizes and switching vaccine types between the first and second shots.

The proposals have generated fierce debate among scientists. Here is the rationale behind, and criticism of, these alternative strategies: