Every single day, people die unexpectedly. They have strokes and heart attacks and seizures. On an average day, 110 people in this country may develop Bell’s palsy, a temporary facial paralysis, and another 274 will develop Guillain-Barré syndrome, a form of paralysis that usually resolves over time. The trigger for these medical events often isn’t known. But when they happen shortly after someone gets a vaccine — especially a new one — well, conclusions will be drawn.

“It is logical for people to say: That person had something done to them and something bad happened in the hours or days after that,” said Art Reingold, chair of the division of epidemiology and biostatistics at UC Berkeley’s School of Public Health. “And if it was you or your family member, you would be inconvincible that that wasn’t true.”

Except, of course, it often isn’t. Heart attacks occur most commonly in the morning, yet we don’t blame breakfast for causing them. A heart attack on the morning after a Covid-19 vaccine, though? That might be another matter.