The novel coronavirus has killed at least 425 people and sickened some 20,000. No vaccine exists. Yet amid this public-health emergency, China is playing power politics at the world’s peril in its treatment of Taiwan.

From 2009 to 2016, the World Health Organization allowed Taiwan to attend its annual policy meetings as a nonvoting observer and sometimes let its representatives participate in technical meetings. But at Beijing’s behest, the WHO has given Taiwan the pariah treatment since Tsai Ing-wen was elected president in 2016. China’s State Council said that Taiwan’s absence from a key WHO meeting last year was “totally caused by the acts” of Ms. Tsai’s Democratic Progressive Party and its “separatist position of ‘Taiwan independence.’”

The WHO has held two emergency meetings since the coronavirus outbreak. Taiwan wasn’t permitted to attend, despite its proximity to China and its handful of confirmed cases. Taiwan often must rely on second-hand information relayed by friendly governments and nongovernmental organizations. Delays are inevitable, though there’s an urgent need for collaboration about potential exposure and the epidemiology of coronavirus. “This will literally impede the response. It’s deeply harmful to not only the citizens of Taiwan but the entire region,” said Lawrence Gostin, faculty director of the O’Neill Institute for National and Global Health Law at Georgetown University.

Last week WHO Director-General Tedros Adhanom Ghebreyesus praised “the seriousness with which China is taking this outbreak, especially the commitment from top leadership, and the transparency they have demonstrated.” Evidence to the contrary continues to grow, undermining the WHO’s credibility.

China’s bullying ought to be intolerable amid the coronavirus outbreak. As the single largest contributor to the WHO, the United States should make that clear to Beijing.