At churches, on cruise ships and even in the White House, superspreading events that can sicken dozens, even hundreds, of people have illustrated the potential for the coronavirus to infect in dramatic bursts. Experts say these large clusters are more than just extreme outliers, but rather the pandemic’s likely main engine of transmission. And understanding where, when and why they happen could help us tame the spread of the virus in the period before a vaccine may be widely available. Research increasingly suggests that the coronavirus SARS-CoV-2 does not fan out evenly across the population, but spreads at the extremes in an almost “all or nothing” pattern. Many studies now suggest the majority of people with Covid-19 barely pass it on to anyone else, but when infections happen they can be explosive and supercharge an outbreak. Then the virus can infect “10, 20, 50, or even more people”, said Benjamin Althouse, research scientist at the University of Washington’s Institute for Disease Modeling. This corresponds to the “80/20 rule” of epidemiology, where 80 percent of cases come from only 20 percent of those infected, but Althouse said this coronavirus may be even more extreme, with 90 percent of cases coming from potentially just 10 percent of carriers. This transmission pattern is like “throwing matches on a pile of kindling”, he told AFP. “You throw one match, it doesn’t ignite. You throw another match, it doesn’t ignite. You throw yet another match, and this time you see flames blaze up,” he said.