A man in Africa who developed Ebola despite a vaccine recovered but suffered a relapse almost six months later which led to 91 new cases before dying. The case, described in the New England Journal of Medicine on Wednesday, adds to evidence that the deadly virus can lurk in the body long after symptoms have ended and that survivors should be monitored for their own well-being and to prevent spread.

It is believed that such relapses, from the 2018-2020 epidemic in the Democratic Republic of the Congo, are rare. This is the first to have clearly generated a large number of new cases.

However, this month, scientists said that a separate outbreak that is currently underway in Guinea appears to be linked to an outbreak in West Africa that ended five years ago. A survivor may have harbored the virus silently for years before spreading it.

“The most important message is that someone can get the disease twice and the second disease can sometimes be worse than the first,” said Dr Placide Mbala-Kingebeni of the University of Kinshasha, who helped research the cases of Congo.

As more and more Ebola outbreaks occur, “we are getting more and more survivors” and the risk posed by relapses increases, he said.

Ebola outbreaks usually start when someone contracts the virus from wildlife. It then spreads from person to person through contact with bodily fluids or contaminated materials. Symptoms may include sudden fever, muscle pain, headache, sore throat, vomiting, diarrhea, rash, and bleeding. Mortality rates vary from 25% to 90%.

The case in the medical journal involved a 25-year-old motorcycle taxi driver who was vaccinated in December 2018 because he had been in contact with someone with Ebola. In June 2019, he developed symptoms and was diagnosed with the disease.

For some reason, the man never developed or lost immunity within six months, said Michael Wiley, a virus expert at Nebraska Medical Center who helped investigate the case.

The man was treated and discharged after twice testing negative for Ebola in his blood. However, semen can harbor the virus for over a year, so men are advised to get tested periodically after recovery. The man had a negative semen test in August but did not return after that.

At the end of November, he again developed symptoms and sought treatment at a health center and from a traditional healer. After worsening, he was sent to a specialized Ebola treatment unit, but died the next day.

Genetic testing showed that the virus causing his new illness was almost identical to his original virus, meaning it was a relapse, not a new infection from another person or d ‘an animal,’ Wiley said. Tests showed the man spread the virus to 29 other people and they spread it to 62 others.

Previously, two health workers who contracted Ebola while treating patients in Africa had the virus long after they recovered – a Scottish nurse in her cerebrospinal fluid and an american doctor in his eyes. But these relapses were discovered quickly and did not lead to new epidemics.

They and man in Africa were all treated with antibodies during their initial infections. Doctors are now theorizing that these patients might not develop a strong enough immune response on their own and might be vulnerable to recurrence once the antibodies wear off.

A few other viruses can hide for long periods of time and cause problems later, such as the one that causes chickenpox, which can reactivate and cause shingles decades after the initial infection.

The news about latent Ebola tells us “absolutely nothing” about the possibility of something similar happening with Covid-19, because “they are totally different viruses,” Wiley said.

Dr Ibrahima Soce Fall, a scientist from the World Health Organization, agrees. “We have yet to see this kind of latency from people who have survived the coronavirus,” he said. Even with Ebola, “after six months most patients completely clear the virus.”