The Democratic Republic of the Congo declared its outbreak of Ebola over on Wednesday, but the danger isn’t gone.

It’s been 42 days since the last new case was reported. It can take 21 days to develop symptoms after having been exposed to the Ebola virus, so 42 days makes for two incubation periods. Congo's health ministry says 53 people were infected and 33 died in the outbreak.

But the danger is not completely over. Research shows that in some cases, Ebola survivors can infect people months later. Men can transmit the virus in their semen and now, doctors have confirmed that a woman who survived the 2014-2016 epidemic in West Africa probably infected her family.

The unusual cluster of cases in Liberia was identified after the woman’s 15-year-old son was diagnosed with Ebola in November 2015. Scientists then tested the rest of his family: the woman, her husband and their three younger sons.

The 15-year-old died a few days later. The father and an 8-year-old boy were positive for Ebola, but both recovered. The couple’s 5-year-old son wasn’t infected.

Doctors found Ebola antibodies in the mother, her breast milk and her 2-month-old baby, suggesting a previous infection and that she passed on protection to her infant son through breastfeeding.

Researchers reported genetic similarities between the viruses taken from the father, the two boys and the strain circulating during the 2014-15 outbreak across Liberia, Guinea and Sierra Leone, which ultimately killed more than 11,000 people in the biggest Ebola epidemic in history.

“We don’t want there to be a sense of complacency with people thinking that just because the outbreak is over, there’s nothing more to be done."

Scientists discovered that the woman had cared for her brother in July 2014, who died after suffering Ebola-like symptoms but before being tested for the disease. The woman later experienced a similar illness, but never sought care.

Several weeks after giving birth to a baby in September 2015, the woman developed problems including fatigue and breathing difficulties. Doctors say that because pregnancy lowers the body’s immune defenses, that may have allowed for the Ebola virus to re-emerge.

“The suspicious illness she had following delivery may have been a re-activation of Ebola, but we have no confirmatory tests,” said Dr. Emily Kainne Dokubo, who led the Ebola response in Liberia for the U.S. Centers for Disease Control and Prevention, and the study’s lead author.

Dokubo said it was possible that the woman infected her husband and two older sons with Ebola when they took care of her — the disease is normally spread through contact with an infected patient’s blood or other bodily fluids. The case report was published online Monday in the journal Lancet Infectious Diseases.

“There isn’t complete evidence to reconstruct what happened, but this is the most likely scenario,” said Lorenzo Subissi, an epidemiologist at Sciensano, a Belgian research institute, who was not part of the study.

Dokubo said such cases of Ebola re-emergence are exceptional, with only two reported instances: a Scots nurse who developed meningitis caused by Ebola hidden in her brain and an American physician who had lingering virus in his eye. In those two cases, the virus did not spread any further.

“We don’t want there to be a sense of complacency with people thinking that just because the outbreak is over, there’s nothing more to be done,” Dokubo said. “There is a risk of viral persistence and people should seek care immediately so that we can pick up any suspicious cases right away and stop a larger outbreak.”