The recommendation by the Centers for Disease Control and Prevention and the Food and Drug Administration to pause use of the Johnson & Johnson coronavirus vaccine — citing six women who developed serious blood clots in their brains after vaccination — could hardly have come at a worse time.

美国疾病预防控制中心和美国食品药品监督管理局建议暂停使用强生新型冠状病毒疫苗，理由是6名妇女在接种该疫苗后出现严重的脑血栓，而这一建议来得正是时候。

This news arrived just as vaccination eligibility was opening up and a whole new tranche of people were making the decision to either get or refuse the stick of a needle. Nearly half the eligible population has received at least one injection. Uptake is still limited by vaccine supply in many places. But as public health authorities try to reach the country’s second half — or at least enough to reach herd immunity — they will eventually be recruiting along a descending path of public enthusiasm. And any news that heightens the impression of risk makes their task harder.

这个消息传来之际，疫苗接种资格正在开放，那些还未接种的人正在做出决定：要么接受，要么拒绝接受接种疫苗。近半数符合条件的人口至少接受过一次注射。在许多地方，疫苗的接种仍然受到疫苗供应量的限制。但是，当公共卫生部门试图在我国下半年达到-或至少足以达到群体免疫-他们最终将沿着公众热情下降的道路上完成工作。任何增加风险印象的新闻都会使他们的任务更加艰巨。

Free riders are people who benefit from the public good but don’t have to pay or sacrifice for it. In the case of a pandemic, free riders are those who enjoy the positive result when other people get vaccinated — lower transmission of the virus and eventual herd protection — but refuse to take a tiny risk and get vaccinated themselves. The challenge comes, of course, when lots of people realize they can be free riders, and the public good is destroyed.

搭便车者是从公共利益中获益，但不必为此付出代价或牺牲的人。在大流行的情况下，搭便车的人是那些在别人接种疫苗时享受积极结果的人——病毒传播率较低，最终起到群体保护作用——但拒绝冒一点风险自己去接种疫苗。当然，当很多人意识到自己可以成为搭便车的人时，挑战就来了，公共利益也就被破坏了。