Confronted with rare cases of blood clots potentially linked to Johnson & Johnson’s COVID-19 vaccine, U.S. health officials faced a delicate task: how to suspend distribution of the shots without setting off alarm about their safety.

It was the just the latest challenge in crisis messaging for officials since the start of the pandemic more than a year ago. The behavior of the new virus, the benefits of masks and the need for school and business closings have all been marked by public confusion, changing guidance and squabbling.

With the J&J shots, the recommended “pause” announced last week was a precautionary measure as government advisers investigated the unusual clots and alerted doctors about how to treat them. But the news was bound to inflame fears.

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