SAO PAULO — Brazil’s yellow fever vaccination efforts have fallen significantly short of their goal, the Health Ministry acknowledged this week, and an official said Friday that more than 16 million people in the targeted population still need to be immunized.

In January, the ministry launched a campaign to vaccinate more than 23 million people in three states affected by the largest outbreak of the mosquito-borne disease in decades. As the outbreak expanded, so, too, did the population officials hoped to reach, and they now want to vaccinate 38 million people in Sao Paulo, Rio de Janeiro and Bahia states.

But those efforts have been dogged by rumors that the vaccine is unsafe or ineffective, and health officials have struggled to effectively combat that misinformation.

So far, they have only reached 57 percent of the targeted population in three states, leaving more than 16 million people unvaccinated, Carla Domingues, the coordinator of the ministry’s national immunization program, said Friday. The ministry had announced in March that it had reached 76 percent of the targeted population, but Domingues said that rate was calculated before the goal was expanded.

The ministry’s goal is to reach 95 percent of the targeted population since the vaccine won’t be appropriate for some people.

Yellow fever has long been endemic in large swaths of Brazil, but it has been advancing in recent years and this is the second outbreak in a row in places where vaccinations for the disease were not routine.

The current outbreak is the largest in more than three decades in Latin America’s largest nation. So far, 1,127 people have been infected; of those, 331 have died. During the 2016-2017 outbreak, more than 770 people were infected after nearly a decade during which Brazil saw fewer than 10 cases each year.

In response to this advance, Brazil decided to offer routine vaccination for the entire country – but it will take about another year to completely roll that out.

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