Most COVID cases don’t spread virus

Overall, 539 (52 percent) of all of Hong Kong’s cases were linked to one of 135 clusters, while 449 cases were sporadically imported and 50 were sporadic local cases not linked to any cluster. And of 349 local infections, 196 were linked to just six superspreading events. In one superspreading event, a single person seems to have infected 73 others in a cluster that eventually included 106 cases across bars where a network of musicians played.

Overall, the researchers calculated that just 20 percent of Hong Kong’s cases were responsible for 80 percent of transmission. A further 10 percent of cases spread the infection to just one or two other people—mostly in household settings. And the remaining 70 percent of cases did not pass the infection to anyone.

Surprisingly, when the researchers looked at the people who were infected in superspreading events but didn’t go on to infect anyone else themselves, only 27 percent ended their infection in quarantine. The authors note that although Hong Kong didn’t have a strict lockdown or stay-at-home order, residents were following social distancing measures, including restrictions on gatherings.