RIO DE JANEIRO — Containment efforts have largely failed. The coronavirus is everywhere. And President Jair Bolsonaro's response to the hundreds of thousands of dead has been a shrug: "Life goes on."

Brazil, hit by the third-most cases in the world, has long seen a vaccine as the only way out. But while wealthier countries have galloped into their vaccination campaigns, Brazil has been stumbling. Mass vaccination still hasn’t begun. Misinformation and vaccine hesitance are rising.

And now, a fresh setback: a vaccine that’s good — but not great.

Days after officials here announced that the vaccine produced by the Chinese company Sinovac — and tested on 12,000 Brazilians — was 78 percent effective in protecting against moderate and severe covid-19 cases, they clarified this week that its efficacy rate among all cases was only 50.4 percent. That exceeds the threshold established by the World Health Organization — but only barely.

The underwhelming results are a setback not only for Brazil, where more people have died of the virus than anywhere else outside the United States, but also for countries everywhere that have pinned their hopes on a vaccine that’s cheap, easily transported and ready for mass production. It also clarified anew the role of global inequality in the spread of the disease.

As wealthier countries deploy vaccines with efficacy rates greater than 90 percent, poorer countries have been left with fewer options. As a result, health analysts warn, the developing world probably will be dealing with the coronavirus for far longer than wealthier nations.

“Brazil is not in a place where it can compete with very rich countries to buy vaccines like the ones by Pfizer and Moderna,” said Natália Pasternak Taschner, a scientist advising health authorities here on the vaccine rollout. “And then to have the capacity to transport them, implement them and maintain them in the required low temperatures — we can’t do it as a developing country.”

Sinovac has defended its vaccine, called CoronaVac, saying it’s effective in preventing severe symptoms and that its efficacy rate could prove higher for the general population than for the medical workers who were its trial participants here.

“The clinical trial population in Brazil is relatively special,” the company said in a statement. “Medical workers aren’t only at the highest risk for disease infection, but are also at highest risk for disease transmission.”

Brazil and other countries plan to use the vaccine as soon as possible. Turkey said Wednesday it had granted CoronaVac emergency authorization. Indonesian President Joko Widodo went on television to receive the country’s first dose.

Turkey and Indonesia announced dramatically different efficacy rates for CoronaVac — 91 percent and 65 percent — based on studies that scientists say were too small to be conclusive.

Sinovac said some of the variation could be attributable to differences in clinical trial setups among the countries. Indonesia’s trial was conducted on members of the general public, not medical workers.

Still, it’s unusual for efficacy to swing so widely across trials, said Arthur Caplan, head of medical ethics at New York University’s Grossman School of Medicine.

“The difference is big enough that you start to wonder: Did they administer them properly?” Caplan said.

The WHO has long warned of the difficulties confronting developing countries trying to secure a vaccine quickly. In his New Year’s address, WHO Director General Tedros Adhanom Ghebreyesus said the organization had secured 2 billion doses of promising vaccines but urgently needed $4 billion to purchase enough doses for low- and lower-middle-income countries.

“To protect the world, we must ensure that all people at risk everywhere — not just in countries who can afford vaccines — are immunized,” he said.

With the Moderna and Pfizer vaccines in short supply, many have bet heavily on China’s vaccines, which President Xi Jinping has declared a “global public good.” Countries including the United Arab Emirates opted for vaccines made by Chinese state-owned pharmaceutical giant Sinopharm, while others, such as Brazil, favored the private-sector vendor Sinovac.

The global struggle has played out painfully in Brazil, where the disease has been devastating and Bolsonaro has encouraged Brazilians to get on with their lives. In the absence of federal leadership, governors and city mayors have established a patchwork of conflicting guidelines and procedures.

In São Paulo state, where more than 48,000 people have died of covid-19, officials have tried on their own to secure the Sinovac vaccine, setting up large-scale clinical trials through the Butantan Institute in São Paulo.

Politics quickly jeopardized the efforts.

Bolsonaro has repeatedly taunted São Paulo Gov. João Doria, a bitter political rival, for his ambitious vaccination plans, undermining trust in the vaccine. The president, who has declared he won’t get the vaccine, has warned Brazilians that they take it at their own risk.

“If you turn into an alligator, it’s your problem,” Bolsonaro said. “If you turn into Superman, grow a beard for some women, or a man starts speaking in a high pitch, [the drugmakers] won’t have anything to do with it.” He has raised the possibility of requiring people to sign waivers before getting injected.

Confidence in vaccines in Brazil has been plunging. Surveys last year found 97 percent of Brazilians believed in the importance of vaccinating children. But now only 72 percent of people in the cities of Rio and São Paulo say they intend to get the coronavirus vaccine.

Brazilians have voiced particular mistrust of CoronaVac, which Bolsonaro’s supporters have attacked with racist and xenophobic language.

But rather than assuage those worries, officials in São Paulo appear to have exacerbated them. The release of data from the clinical trials in Brazil was repeatedly delayed in recent weeks. Doria, who is widely believed to be planning a run at the presidency in 2022, made bold promises he has failed or struggled to keep. And when officials finally released numbers on CoronaVac, they were exceedingly sparse, without any mention of antibodies — and later muddied by the fuller picture.

Last week, officials said the vaccine was 100 percent effective in protecting against deaths and hospitalizations. They said it was 78 percent effective in protecting against severe infections. Doria, for his part, boasted in a statement that it was “78 to 100 percent effective against covid-19.”

But this week, Butantan officials, under increasing pressure for more transparency, conceded the efficacy rate fell to 50 percent when accounting for patients with “very mild” symptoms.

“The errors in communication have taken a situation that was already complicated and made it much more complicated,” said João Henrique Rafael Junior, a researcher at the University of São Paulo who tracks vaccine-related misinformation. Disinformation groups, he said, “are now using that to distort the picture and make their own narrative.”

Butantan did not respond to a request for comment.

Doria defended the vaccine. “Renowned scientists declared their satisfaction with the presentation of the clinical studies in safety and efficacy for the Butantan vaccine,” he said in a statement. “The appeal of science is for the end of polarization and the beginning of vaccination.”

But the end of vaccination will take longer to reach with a vaccine that works only half the time, even if it largely protects people from severe reactions to the virus.

“To realistically achieve herd immunity, we would need to vaccinate pretty much everyone,” said Pedro Hallal, an epidemiologist at the Federal University of Pelotas. “If you have a vaccine with 50 percent efficacy, you need full coverage to stop the virus from circulating. There is no margin for error.”

Dou reported from Detroit. Heloísa Traiano in Rio de Janeiro, Kareem Fahim in Istanbul and Lyric Li in Seoul contributed to this report.