Many were comatose, and those who were conscious had bouts of nausea, vomiting, and hyperventilation. Scarier still, some experienced kidney failure and vision problems. A world that was once crystal clear now looked like they were watching TV on a station with bad reception. Then their sight failed completely.

When these patients began trickling into emergency rooms at hospitals across Iran in late February, doctors struggled to make sense of what was happening. But Hossein Hassanian-Moghaddam, a clinical toxicologist at Loghman Hakim Hospital in Tehran, had seen this before. Even as cases of the novel coronavirus tore through Iran, a second epidemic emerged in its shadow. By mid-March, an outbreak of methanol poisoning gripped the country.

As the coronavirus began to spread