Scientists have found evidence that a woman can harbour the Ebola virus for more than a year and then infect others for the first time.

The discovery involved transmission within a Liberian family in the closing days of the West African epidemic that lasted from December 2014 to mid-2016. More than 28,600 people were infected and 11,325 died.

The episode raises new medical questions. Scientists do not know how the virus hid inside the woman for 13 months before re-emerging in lethal form.

However, because she fell ill shortly after giving birth, experts believe the immune suppression that normally occurs in pregnancy may have triggered a relapse.

The case, published by Lancet Infectious Diseases, also worried experts because fear of Ebola survivors and discrimination against them persists in Africa and the notion that a female survivor can pass on the virus could worsen that.

In the past, although bits of virus have been found in the breast milk and spinal fluid of women who recover, only male survivors have been shown to infect anyone. Those transmissions were through sex – the virus is known to persist in semen for two years.

The family cluster came to light in November 2015, six months after Liberia had declared its outbreak over – prematurely, it turned out.

A 15-year-old boy, the woman’s oldest son, was hospitalised vomiting blood. He tested positive for Ebola and, despite intensive treatment, died 10 days after his symptoms first appeared.

As soon as he tested positive, contact-tracers brought his whole family, including his 33-year-old mother, his 40-year-old father and his three younger brothers, aged 8, 5 and two months, in for observation and testing.

The family also became the first participants in a clinical trial of a new Ebola vaccine, said Dr Emily Kainne Dokubo, an epidemiologist at the US Centres for Disease Control and Prevention (CDC) who was then the leader of the agency’s Ebola response in Liberia and is the lead author of the Lancet study.

All 120 people with any recent contact with the family were vaccinated, she said. None fell ill, and that helped prove the Merck vaccine works.

This year, the vaccine was used to defeat the most recent Ebola outbreak, which took place in the Democratic Republic of Congo. About 3,200 people were vaccinated, and new cases faded out after only about three months. The director-general of the World Health Organisation will officially declare it over later this week.

In Liberia, after the 15-year-old died, blood tests showed that his father and 8-year-old brother had Ebola. With treatment, both recovered.

The five-year-old apparently was never infected.

Life after Ebola: a community rebuilds in Sierra Leone Show all 27 1 /27 Life after Ebola: a community rebuilds in Sierra Leone Life after Ebola: a community rebuilds in Sierra Leone Haja Bobor, 31 ‘During Ebola, they quarantined areas. My husband was at Kailahun and couldn’t cross the boundary, so we were separated. They taught us how to wash our hands and we were all washing our hands every day; even my children were washing their hands.’ Haja is the mother of three surviving children, two of her children died from diarrhoea WaterAid Life after Ebola: a community rebuilds in Sierra Leone Aruna Bockarie, 24 ‘This is the finished toilet that we have built in our compound, I am very happy to have my own toilet and I will be proud to use it’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Aruna Bockarie, 24 ‘All the parents came together and built a school in the village, we have just opened the school. The children are at assembly with no uniforms. I am the teacher at the school so I took this photo to show how we have been working hard for our children to be educated’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Haja Bobor, 31 ‘Here is my son, Sessay (left), with his friends. I was happy to snap them. I have given birth to six children, but only three are still alive. The first one I lost was three years ago, and the second was two years ago. Four months ago I lost Senior Lahai. He was six months old and was affected by a runny stomach and a rising body temperature’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Haja Bobor, 31 ‘Four months ago I lost Senior Lahai. He was six months old and was affected by a runny stomach and a rising body temperature. He was really, really sick, he wasn't even taking breast milk, and he died. My heart was broken. My baby used to be strong. He was able to sit by himself and was just starting to practise to crawl and reach for things. He laughed a lot when I played with him, I’d clap and dance. I have a happy moment when he started sitting by himself and learning to crawl. Those are the happy moments that makes a mother most happy. The moment I remember most about Lahai was when he was breastfeeding and was playing with my neck and chin with his hand. I look to the future and hope that such things won't happen again, and that God will give me children that stay with me’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Aruna Bockarie, 24 ‘My step brother Ibrahim is building our toilet with loamy soil because we don’t have cement. WaterAid taught us about good sanitation and I want to show that we are now building our own toilets so that we will not go to the bush or use the stream as a toilet that is why I took this photo’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Aruna, 33 Washing in the stream: ‘When we came here the water system was very bad. I know that when I drink dirty water I get sick. We are getting diarrhoea because we are drinking that type of water. If I am sick I am not able to earn money because I am not able to go to work, and I have to stay at home, which is very difficult for me’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Tailu Yajah ‘These are the contractors that came to build the water well, and they are mixing the stones and the cement to build the cover of the well’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Tailu Yajah ‘I started tree climbing when I was living with my grandmother and she was trying to get some palm kernels and process them to make the oil that we use. I didn’t like doing the processing part so I decided to climb the trees to do the harvest instead. Tree climbing is very difficult. At times you can be confronted by a snake, as you are going up you just see one and it will hiss at you. If you are not strong you are going to fall out of the tree, and could die! I am just doing it for necessity sake. I don’t want to do this job really, but at the moment I have no other means of making money, so I have no choice but to do this to manage my family’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Haja Bobor, 31 ‘They killed my uncle during the war. I was not in this village during the war; I was in Guinea. Just after the war, my mother asked me to come back home. There were no houses when I returned; it had all been destroyed’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Tailu Yajah ‘This is my son Bockarie. He reminds me of his mother, who is not presently here with me, and he resembles me. Recently my son was very sick and we had to take him to the clinic to get treatment. Even getting to the clinic costs money. I didn't have any money, so I had to borrow money from the community people so I could take him to the hospital. Having very good drinking water would ease the issues with having to take people to the hospital because of illness, and the problem of finding the money to manage that’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Tailu Yujah ‘Sidique is 21 years old, he is my daughter’s husband and is drinking from the stream we use to fetch water. Our forefathers created this village, and the water was good. They covered it with a concrete box to keep it safe, but all of that fell down during the war, and afterwards no one could repair it. The water is not good here now and I have worms as a result. It will be very good to have clean water; it would give us a long life. If you have good drinking water, then your life is safe, but if you don’t then your life is not secure. Having good drinking water would ease the issues with having to take people to the hospital because of illness, and the problem of finding the money to manage that’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Matu, 40 ‘We the women of this village are experiencing the problems with lack of water and we pray that things will change. The rain washes everything, including faeces into the water. The children get diarrhoea from the water. With clean water, I would be clean and would not suffer from sickness’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Matu, 40 ‘This is my brother’s wife, she is holding both her daughter and my granddaughter’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Matu, 40 Matu is the life and soul of the village of Tombohuaun. She is a traditional birth attendant and plays an important role within the women’s society. Matu suffers from poor health; she has stomach problems caused by the dirty water WaterAid Life after Ebola: a community rebuilds in Sierra Leone Amadou Kokoyeh (Bush Chicken), 8 ‘My name is Amadou Kokoyeh, but I am more familiar with Kokoyeh [Bush Chicken]. The name Kokoyeh was given to me by father’s older brother. It’s meant to be a bird that is in the bush and mostly eats other people’s groundnuts when they plant them.” WaterAid Life after Ebola: a community rebuilds in Sierra Leone Amadou Kokoyeh (Bush Chicken), 8 ‘This is my father helping to dig the water well, so that we will have clean water to drink. I am happy because we are going to have a well in my village. I don’t think the water we currently collect from the muddy spring is good for drinking because it is exposed, and leaves and other things fall in it. I also get water down there with my mum, and sometimes I go with the other kids. Sometimes when I drink it, I have a stomach pain, and it also brings me headache. I have got sick from that, and I was taken to the health centre’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Amadou Kokoyeh (Bush Chicken), 8 ‘This is my family – my mother, father and younger brother. When I’m not with them this picture will make me feel closer to them’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Amadou Kokoyeh (Bush Chicken), 8 ‘Moserie Yajah was lying down in the grass, and asked me to get a shot of him. At the moment, every day people ask me to get a photo of them. I feel very happy when people ask for a picture. What I love most to get a shot of is people that are well dressed, sitting in a chair or in a very comfortable area that I can snap’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Amadou Kokoyeh (Bush Chicken), 8 ‘We were going down to Matu’s place, and my friends and brother decided to cover themselves with that fishing net, and asked me to take a shot of them. The fishing net was taken from Ginnah’s mother (Massah) and I think the picture is really good. I like the photo mainly because they are standing close to the wash yard, where people go to heat their water and wash. I love it because they are all my brothers, and we look out for each other’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Amadou Kokoyeh (Bush Chicken), 8 ‘I love this picture. I took this photo of Bockarie when he was drinking water. The water was collected from the muddy spring where everyone collects water. I don’t think it is good for drinking because it is exposed, and leaves and other things fall in it. I also get water down there with my mum, and sometimes I go with the other kids. Sometimes when I drink it, I have a stomach pain, and it also brings me headache. I have got sick from that, and I was taken to the health centre. If it rains, we harvest rainwater’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Amadou Kokoyeh (Bush Chicken), 8 ‘This is my cousin Papay; we are very close – he lives nearby and we spend lots of time together. In this picture he is messing around. On his head is what our fathers make to catch fish in small streams. We then eat some fish and they sell the rest. It is important for our survival’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Kempah Ginnah, 42 ‘The community people helping to build the water well, I was glad about this, that is why I took this photo.’ Kempah is a youth leader and mechanic from Tombohuaun WaterAid Life after Ebola: a community rebuilds in Sierra Leone Kempah Ginnah, 42 ‘These children are our next of kin, my children and their friends. They are wonderful children’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Jeneba, 13 ‘Here, my father, brothers and aunt are separating cocoa fruit from pods. By selling cocoa, my family earns enough to pay my school fees’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Haja Bobor, 31 ‘We have now built a small school in our village. This is inside the class for my children’s first day in school. I took this picture to show them in the future so they will know that I want them to be educated and also free from diseases’ WaterAid Life after Ebola: a community rebuilds in Sierra Leone Haja Bobor, 31 ‘This is my Aunt Mamie Ansumana. She is 40 and is a farmer. She loves going to the farm and likes to smile. She looked after me when my children died. The dirty water caused the death of two of my children; I don’t want anything to happen to the others. She took me from the room where Senior Lahai died to her own room. I slept in her room for some time. I want to thank to her because she is still taking care of us’ WaterAid

Neither the mother nor the new baby had virus in their blood but, rather mysteriously, both had antibodies against it. That suggested the mother had an earlier infection and that the baby had absorbed protective antibodies through breast-feeding.

Dokubo described what she and her CDC colleagues believe happened:

In July, 2014, soon after Ebola first reached Liberia from Guinea, the mother had cared for her brother, a nurse’s aide dying of an unknown illness. She was pregnant; she soon fell ill and miscarried, but slowly recovered.

Neither she nor her brother went to one of the new Ebola treatment units then being set up, so they never had Ebola tests.

“That was not uncommon, with all the stigma and fear at the time,” Dr Dokubo said.

Thirteen months later, in September, 2015, she gave birth to a healthy boy.

The following month she was hospitalised with fatigue, shortness of breath and swollen legs. Liberia had been declared Ebola-free in May, so she was not tested for it. Instead, she was treated for malaria and given blood transfusions because she was anaemic, and sent home after three days. (The hospital tested its stored blood and none had Ebola virus or antibodies, the study said.)

But pregnancy lowers mothers’ immune systems to protect foetuses from rejection, and Dokubo said pregnancy had probably unleashed a hidden reservoir of dormant virus within the woman; tests did not establish where that reservoir might be.

There was no evidence of sexual transmission; the woman’s husband and two elder sons probably became infected while caring for her, Dokubo said.

Although the case is rare and highly unusual among the thousands of Ebola survivors in West Africa, it means that countries cannot become complacent even when outbreaks seem to be over, Dokubo said.

Also, she added, survivors must be tested for Ebola if they fall ill, even if they lack common Ebola symptoms.

In an editorial accompanying the Lancet article, Lorenzo Subissi, an Ebola expert at Sciensano, Belgium’s public health institute, said the new study “could lead to additional stigma around survivors”.

Survivors are often driven out of their villages or neighbourhoods because people fear they may be infectious, so Subissi suggested that vaccination be used both to stop outbreaks and to calm the fears that lead to stigmatisation and abuse of survivors.