Dr. Paul McKay works at a fume hood inside a laboratory at Imperial College London, one of several labs worldwide developing potential coronavirus vaccines based on using messenger RNA to trigger the immune system. (Imperial College London/Thomas Angus/Reuters)

LONDON — In the global race to beat back the coronavirus pandemic, scientists in Britain, Germany, China and the United States are pushing to develop, and possibly manufacture, vaccines in a completely new way.

This promising — but unproven — new generation of vaccine technologies is based on deploying a tiny snip of genetic code called messenger RNA to trigger the immune system. It has never before been approved for use.