Africa was declared free of wild poliovirus just two years ago. Now, it's got a new outbreak on its hands. Mozambique reported its first case since 1992 on Wednesday, according to the World Health Organization.

It's the second case to be detected on the continent this year, after Malawi reported Africa's first case in five years in February.

The case in Mozambique was detected in a child in the country's northeastern Tete province, according to the WHO. Like the case reported earlier this year in Malawi, genomic sequencing shows it is linked to a strain that circulated in Pakistan in 2019.

A nationwide vaccination campaign launched in Malawi in March targeting children aged 5 years and younger. Mozambique also recently carried out its own campaign, the WHO said.

“The detection of another case of wild polio virus in Africa is greatly concerning, even if it’s unsurprising given the recent outbreak in Malawi," said Matshidiso Moeti, World Health Organization Regional Director for Africa, in a press statement. "However, it shows how dangerous this virus is and how quickly it can spread."

First case in years

Laboratory analysis linked the strain discovered in February to one that has been reported in Sindh Province in Pakistan, where polio remains endemic, the WHO said. Afghanistan is the only other country with endemic polio.

Because it is an imported case from Pakistan, Africa will not lose its polio-free certification status, the WHO added.

The last case of wild polio virus in Africa was identified in northern Nigeria in 2016, said Modjirom Ndoutabe, polio coordinator in the WHO Regional Office for Africa, in a press statement. There were only five cases globally in 2021.

Africa has been considered free of polio since August 2020. 

For a country to be certified polio-free, it must have had no wild polio cases for three consecutive years.

Polio risk ongoing

No country is immune to imported cases of polio, Moeti said.

"As long as wild polio exists anywhere in the world all countries remain at risk of importation of the virus," Moeti said.

The coronavirus pandemic may have also caused some young children to miss their polio vaccinations, Nicola Stonehouse, a professor of molecular virology at the University of Leeds in the UK, told DW.

The WHO is helping to supplement vaccinations in Malawi, as well as support the risk assessment and outbreak response and ramp up surveillance of polio in neighboring countries.

What is polio?

Polio is a highly transmissible virus most often spread via the stool of an infected person, usually through contaminated water or food. It can also be spread via oral or nasal secretions. The virus mainly affects children under 5 years of age.

There is no cure for the symptoms of polio. Most people infected with the virus have no symptoms at all, according to the US Centers for Disease Control and Prevention (CDC). About one in four people will have mild symptoms that last two to five days, such as a sore throat, fever, fatigue, nausea, headache or stomach pain.

The virus usually stays in the gut, but when it spreads to other parts of the body it can cause more serious symptoms affecting the brain and spinal cord. These symptoms only occur in a small percentage of cases and can cause paralysis of some body parts, which can result in death if the breathing muscles become paralyzed, for example. This is known as paralytic polio.

Eradicating polio

There are three types of poliovirus. Polio type 2 is considered eradicated, but there is no cross-protection if a person has been infected with one type. This is why vaccination is the best protection, health officials say.

The first polio vaccines were developed in the 1950s, and vaccination programs have drastically reduced case numbers since. In the 1980s, the estimated number of paralytic polio cases worldwide was more than 350,000 per year. By 2016, there were just 42, according to Our World in Data, a scientific online publication.

Wild polio is a naturally occurring virus that circulates the population, whereas a small number of paralytic polio cases are caused by the oral polio vaccine.

This oral vaccine is still used in some regions because it is cheap and doesn't require a cold chain, which can be difficult to facilitate in some countries, said Stonehouse.

"When you're looking at Afghanistan and Pakistan, a lot of the problems are in those incredibly hard-to-reach areas in terms of physical geography — people who live in remote communities," Stonehouse told DW.

The most commonly used polio vaccine is administered through injection.

Once all wild polio has been eradicated, the oral polio vaccine will no longer be used, according to the WHO.

Edited by: Clare Roth

This is an updated version of an article originally published on March 17, 2022.