As a mysterious virus spread through Wuhan last month, the World Health Organization had a message: China has got this.

And as the coronavirus swept across the Chinese heartland and jumped to other nations, WHO's director general, Tedros Adhanom Ghebreyesus, applauded the "transparency" of the Chinese response.

Even as evidence mounted that Chinese officials had silenced whistleblowers and undercounted cases, Tedros took a moment to extol the leadership of Chinese President Xi Jinping.

Now — more than a month into an escalating global health crisis — there are questions about whether the WHO's praise in the early weeks created a false sense of security that potentially spurred the virus' spread.

"We were deceived," said Lawrence Gostin, a professor of global health law at Georgetown University who also provides technical assistance to WHO.

"Myself and other public health experts, based on what the World Health Organization and China were saying, reassured the public that this was not serious, that we could bring this under control," he said.

Experts familiar with the workings of WHO, including current and former advisers, stressed that careful diplomacy and public praise can keep countries in crisis from shutting out the world.

The agency learned valuable lessons from the 2002 outbreak of severe acute respiratory syndrome (SARS), which China initially tried to cover up.

But some fear that WHO's embrace of China's numbers and assessments in the early stages of this outbreak, as well as its ongoing praise for the country's response, are testing the agency's global credibility right when it needs it most.

"I'm concerned about whether they can actually assume leadership effectively in terms of the international response," said Yanzhong Huang, a senior fellow for global health at the Council on Foreign Relations.

"People trust the organization to be the guardian of global health because it is politically neutral and has expertise."

In late December, rumors of a mysterious virus started circulating on Chinese social media. China notified WHO on Dec. 31 that there was a pneumonia of unknown cause in Wuhan. Based on Chinese data, WHO issued a Jan. 5 statement saying there were 44 cases and no evidence of person-to-person transmission.

But a Washington Post reconstruction of events showed that by Jan. 5, some Wuhan authorities knew that doctors were discussing the spread of a SARS-like virus. For this, they were detained and denounced.

It also found that local officials undercounted cases.

In late January, China moved from denial to drastic action.

On Jan. 20, with 400 million people about to travel for the Lunar New Year holiday, officials confirmed what many had long suspected: The virus could spread person to person.

Authorities started to seal off Wuhan, a city of 11 million, canceling some flights, trains and suspending public transportation.

In Geneva, an emergency panel convened to discuss the situation and decide whether to declare a public health emergency of international concern, or PHEIC, which signals "serious, unusual or unexpected" health crisis "that poses a public health risk to other countries through international spread."

On Jan. 22, Tedros applauded China's efforts. "What they are doing is a very, very strong measure and with full commitment," he said.

The comment surprised public health experts because travel bans can create panic and make things harder for first responders.

On Jan. 23, China announced it was expanding the quarantine to other cities — and millions more people.

Later the same day, in Geneva, WHO decided against declaring a PHEIC.

Asked about China's quarantine, Tedros demurred.

"At end of the day, a sovereign country has the autonomy to do what it thinks is right," he said, adding that he hoped it would be short.

On Jan. 30, WHO declared a PHEIC, finally acknowledging the risk the Wuhan outbreak posed to other countries. "The Chinese government is to be congratulated for the extraordinary measures it has taken to contain the outbreak," Tedros said.

Some experts have defended the comments.

"WHO has really tricky balancing act," said Devi Sridhar, a professor of global public health at the University of Edinburgh. "If that means praising China publicly, that's what he has to do."

Others worried that it could shake faith in the U.N. body.

Praising China's leaders "is not a bad idea, but do you want to do it in a professional and credible way," said the Council on Foreign Relations' Huang.

At a new conference on Thursday, Tedros was asked, again, about China.

He defended China's handling of the epidemic, saying, "It is very difficult, given the facts, to say that China was hiding."