Image copyright Getty Images Image caption The WHO confirmed that Zika virus caused microcephaly or small brains in babies

There's another big election coming up which will have an impact on hundreds of millions of people all around world - but you probably haven't heard anything about it.

Health ministers and officials from 194 countries are due to vote for a new director general of the World Health Organization in Geneva on Tuesday.

The UN agency, founded in 1948, describes itself as the "global guardian of public health", but it lost a great deal of credibility and trust over its handling of the Ebola crisis in 2014.

The new boss could make or break the WHO, which is still trying to prove it is fit for purpose after admitting it was slow to respond to what became the worst Ebola outbreak in history.

However, dealing with epidemics is just part of what WHO does.

Its stated goal is to ensure "the highest attainable level of health for all people".

In practice, that means everything from trying to wipe out deadly diseases for good, to trying to deal with the growing number of obesity and diabetes epidemics, to reducing deaths on the roads and saving the lives of mothers and babies during childbirth.

WHO: Six big moments

Led a mass vaccination campaign which eradicated smallpox in 1979

In 1995 it launched a tuberculosis (TB) control strategy which saved more than 35 million lives

By 2006, the number of children dying before their fifth birthday dropped below 10 million for the first time

In 2008, it strengthened its focus on diseases such as heart disease and cancer

It declared Ebola an international public health emergency in 2014

It confirmed that Zika causes brain damage in babies born to infected mothers in 2016

Heading an organisation responsible for the health of all 7.3 billion people on earth is no small task.

"The word 'health' itself is a burden that it carries," said Devi Sridhar, professor of global public health at the University of Edinburgh.

"Improving health worldwide can mean so many things, from mental health to malaria to unintentional injuries… to cancer.

"It's very hard for one agency, with a very limited and very constrained budget - of around $2bn every year - to achieve all those things. "

Consensus and vision

Prof Sridhar, who has recently written a book looking at WHO funding, said the US's health protection agency, the CDC, has a budget more than three times that of the WHO.

She also said most of it comes from donors who earmark their funding for specific projects.

Only around 20% of the WHO budget comes from compulsory contributions from member states, she said.

Whoever gets the top job will have to be the consummate politician. They will have to get country leaders on board with big - often expensive - global health objectives, while also being above politics and not beholden to the special interests of any particular country.

"There have been two types of leader at the WHO in the past," said Prof David Heymann, a former assistant director at the WHO.

"Some have tried to build consensus between 194 member countries, then try to implement what those countries have said. Others have been leaders who have been out in front with a vision, and tried to pull 194 countries along with that vision."

There are three candidates left in the running for the $241,000-a-year job.

The vote will take place at the annual World Health Assembly in Geneva. Whoever is elected will serve a minimum five-year term.

Who are the candidates for the job?

Image copyright Tedros Adhanom Image caption Dr Tedros Adhanom Ghebreyesus, a former health and foreign minister in the Ethiopian government

Dr Tedros Adhanom Ghebreyesus

"I was born into a poor family. When I was seven, I lost my younger brother, probably to measles. I survived by chance, but it could have been me.

"For me, this position is about standing up for the rights of the poor.

"If I became director general, I would be very vocal on the issue of universal healthcare.

"We complain about emergencies or epidemics, worried it may come to our country. But if we ensure universal health coverage, we can resolve all of those issues.

"Inequity is a central challenge. The world has all the resources to save every life, as long as we believe every life is important.

"Those who have, do not care for the have-nots, and unless we confront that reality honestly, I don't think we will make progress."

Image copyright Heartfelt Image caption Dr Sania Nishtar, cardiologist who set up Heartfelt, which works to improve health systems in Pakistan

Dr Sania Nishtar

"I was born and brought up in Peshawar on the Afghan border in Pakistan. I was raised in a progressive family. My father encouraged us to swim in the summer and play golf. I was a local golf champion by the time I was 16.

"When I was 15, my father passed away silently in his sleep - I think that was a turning point in my life.

"I trained as a cardiologist and I became very disillusioned with the disparity of care between the rich and the poor.

"My vision for this role centres on regaining the WHO's primacy, and ensuring that it has the world's trust as its lead health agency.

"Since the Ebola outbreak, the WHO has come under heavy criticism for its inability to... exercise stewardship during health emergencies.

"I want to make the organisation more accountable and transparent.

"I want it to focus on its core roles, rather than doing everything under the sun, in a half-baked way. I would lead the WHO very differently."

Image copyright David Nabbaro Image caption Dr David Nabarro, born in the UK, is UN special adviser on the Sustainable Development goals and is former UN Envoy for Ebola

Dr David Nabarro

"My parents are both doctors, and probably because of their influence, I started working outside the UK.

"It was when I was working in Nepal in 1989, that I found how malnutrition and disease were most likely to come from households that faced particularly difficult circumstances in terms of income, the status of women and their access to sanitation and water.

"It seemed to me blindingly obvious that I had to work on the underlying determinants of health.

"My first priority if I become director general of the WHO, is to focus on universal health coverage - everybody being able to access healthcare when and where they need it.

"My second priority is to make sure people can be defended against outbreaks of disease.

"Thirdly, we are seeing increasing levels of diabetes, heart disease and mental ill-health. These kinds of non-communicable conditions could be prevented by better work across governments and society."

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