The scientific understanding of the disease was broadly the same the world over. But in some instances, scientific disagreements did have repercussions for the preventive tactics chosen. The authorities there accepted Traditional Chinese Medicine as a tool against Covid-19 in a way not true elsewhere. Herd immunity was the belief that if the disease were allowed to run through the population, killing many in the process, the outcome would be broad immunity among the survivors. That would bring the pandemic to a halt. Some nations seem to have toyed with this strategy, though the increased mortality it would cause was politically hard to stomach. Asymptomatic carriers were the infected who spread the disease even though they did not themselves suffer any apparent ill consequences. They could be identified only through widespread testing and posed dangers to others since no one knew who was an asymptomatic carrier. Some people and places were thought to be superspreaders, conveying the disease to many more people than would ordinarily be true. If they could be identified, the payoff in preventive terms was great. Masks, finally, were an initially controversial means of prevention that gradually gained recognition and acceptance. Nonetheless, their use remained a suspect technique, disregarded by many.