News that Johnson & Johnson has paused its COVID-19 vaccine trials comes a month after British regulators put on hold the trial of a vaccine by AstraZeneca. Vaccine developers say these temporary halts show that the trials are being done properly, that it goes with the territory. The vaccine-skeptic public might view it differently. Marco Werman speaks with Polly Roy, chair of virology at the London School of Hygiene and Tropical Medicine.