The African continent was declared free from wild polio on Tuesday, four years after the last cases appeared in northeastern Nigeria.

The official announcement was made in a videoconference with WHO director-general Tedros Adhanom Ghebreyesus. Notables like philanthropist and Microsoft founder Bill Gates were also present in the conference.

Poliomyelitis, or ‘wild polio’ is a severely contagious disease which attacks the spinal cord and causes irreversible paralysis in children.

As late as 1988, the WHO had counted 350,000 cases globally. In 1996, there were more than 70,000 cases in Africa alone.

"Happiness is an understatement. We've been on this marathon for over 30 years," said Tunji Funsho, a Nigerian doctor and local anti-polio coordinator for Rotary International. He said that the virus’s defeat in Africa marked an important stepping stone in the total eradication of the disease at the global level. "It's a real achievement, I feel joy and relief at the same time," he added.

With collective global effort and financial backing - almost $19 billion over 30 years - only 87 cases have been reported this year from two countries - Afghanistan and Pakistan.

Nigeria, with a population of 200 million, was a trouble-spot till the early 2000s. In the northern Muslim-majority areas of the country, vaccine campaigns had to be halted in 2003-2004 due to Islamic extremists who claimed that the vaccination was a vast conspiracy to sterilise young Muslims.

Help was sought from traditional chiefs and religious leaders to convince the populations that the vaccine was safe.

The emergence of another violent Islamist group Boko Haram in 2009, caused a further rupture in the programme. In 2016, four new cases were discovered in Borno state in the northeast, which was at the centre of the conflict. "At the time, we couldn't reach two-thirds of the children of Borno state - 400,000 children couldn't access the vaccine," said Dr Funsho.

Vaccination teams worked under the protection of the Nigerian army and local self-defence militias in these conflicted regions.

For areas under full control of the jihadists, the WHO and its partners intercepted people along market and transport routes in a bid to spread medical awareness, and to recruit ‘health informants’ who could tell them about any cases of the disease which may have been reported.

"We built a pact of trust with these populations, for instance by giving them free medical supplies," said Dr Audu.

Today, it is estimated that about 30,000 children are still inaccessible. However, scientists consider that the number is too low to allow for an epidemic to break out.

Despite the "extreme happiness and pride" felt by Dr Audu at this achievement, he says that he will never fail to remember the 20 or more medical personnel and volunteers who were killed for the cause in northeast Nigeria in the past few years.

The challenge that remains now is to ensure that no new polio cases arrive from Afghanistan or Pakistan, and that vaccinations across the continent continue to protect children from this vicious infection.

"Before we couldn't sleep at all. Now we will sleep with one eye open," said Dr Funsho.