With shortages hitting vaccination sites from San Francisco to San Diego, news that Johnson and Johnson’s COVID-19 vaccine could win emergency authorization this week comes as a relief to health officials worried about the spread of dangerous new variants, and raises hopes there could be enough doses this spring to vaccinate anyone who wants a shot. Doctors Scott Gottlieb of the American Enterprise Institute and Mark McClellan of Duke University’s health policy center, both former Food and Drug Administration commissioners, wrote earlier this month that health officials should prepare for a spring vaccine glut — and prepare a campaign to promote the vaccines’ safety.