An unparalleled Ebola vaccination programme in the Democratic Republic of the Congo has become engulfed in allegations of impropriety, amid claims that women are being asked for sexual favours in exchange for treatment.

Research by several NGOs has revealed that a deep mistrust of health workers is rife in DRC and gender-based violence is believed to have increased since the start of the Ebola outbreak in August.

The research, presented at a national taskforce meeting in Beni, follows calls by international health experts urging the World Health Organization to consider issuing a global alert in relation to the outbreak. The experimental vaccine has been described by the WHO as “highly, highly efficacious” and hopes have been pinned on it controlling the outbreak.

The meeting was told that multiple respondents in one study had raised concerns over individuals offering Ebola-related services, such as vaccinations, in exchange for sexual favours.

The risk of exploitation by frontline Ebola workers was also mentioned by several focus groups.

In a statement, the Ministry of Health said some participants in focus groups had “expressed concerns about women and girls being offered Ebola-related services in exchange for sexual favours.”

Claiming that further analysis has since shown that the vaccination was not specifically mentioned in the discussions, the ministry added: “More importantly, no women reported individual cases of sexual exploitation to the IRC during the focus groups. These women and girls expressed their fears and concerns about the Ebola response considering the social and security context they live in.”

Concerns were raised over a reported increase in stigma and violence facing women. Some women are blamed for failing to prevent the spread of the disease, according to the research by the International Rescue Committee (IRC), whose study was cited in the presentation.

Women, who are responsible for caring for the sick and ensuring that children wash their hands, faced a rising workload, with many feeling traumatised and exhausted, the recent meeting was told. One participant in a focus group said women are isolated during their periods, and are being accused of having the virus.

The IRC has since said those claims were based on preliminary findings. The charity, which consulted more than 30 focus groups, added in a statement that it is still analysing research: “We will take the findings and work with partners to address concerns raised and ensure that women and girls are protected.”

Trina Helderman, senior health and nutrition adviser for Medair’s global emergency response team, said the Ebola response should have established a higher standard of protection for women.

“This region of DRC has a long history of sexual violence and exploitation of women and girls. Though shocking, this is an issue that could have been anticipated,” said Helderman. “Humanitarian actors should have been more prepared to put safety measures in place to prevent this from happening.”

On Thursday, the health ministry urged people to report anyone offering services such as vaccinations or other treatment in exchange for money.

The ministry said it was aware of separate rumours, spread on social media, that women working on the Ebola response had been given jobs in exchange for sexual favours. In a statement, it said it took such claims seriously, and advised that women should only meet with recruiters wearing an official badge.

The warnings come as international health experts urged the WHO to consider issuing a global alert in relation to the outbreak. Writing in the Lancet, they said the response had been complicated by a “storm of detrimental factors”, including political instability, conflict and large numbers of people on the move.

Since August, there have been 811 Ebola cases, and 510 deaths as a result of the virus. The WHO has warned that there is a very high risk of the outbreak spreading not only across DRC but to Uganda, Rwanda and South Sudan. There are also concerns that the source of transmission is unclear in one in five cases.

Suspicion of authorities and health agencies has further hampered efforts to contain the response, said Eva Erlach, of the International Federation of Red Cross and Red Crescent Societies. The agency has analysed feedback from thousands of people living in Ebola-affected areas.

“Across all locations there are lots and lots of people who do not think that Ebola is real, that it is just a way for humanitarian organisations to make money, or that it was just used to postpone elections,” said Erlach.

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Last week, agencies were urged to work closely with women’s groups and local community leaders to build trust in services.

Tarik Jasarevic, a spokesman for the WHO, which supports the Ebola response, said most community engagement activities are already led by national DRC experts who work closely with local networks. There are around 20 dialects spoken in North Kivu and Ituri, he added.

“Together, we continually adapt and work to improve our response to adjust to local challenges in this delicate social, political, economic context,” he said.

Jasarevic added that sexual exploitation is a grave concern, and said the agency continually monitors its services.

“A large part of the communication effort with communities is to inform them that all Ebola services are free,” he said. “We will continue to check and improve measures we have in place to prevent, monitor and report on any such incidents. More can always be done.”

• This article was amended on 13 February 2019 to add in a statement provided by the DRC’s Ministry of Health after publication.