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The East African nation of Malawi on Monday will launch a mass vaccination campaign against polio, organizers say, the first of four planned rounds of vaccination in the region meant to prevent the spread of the crippling virus.

The effort is a response to the discovery in February that a 4-year-old girl who lives on the outskirts of the country’s capital, Lilongwe, was stricken by type 1 polio — Malawi’s first polio case in three decades and the continent’s first since being declared free of wild polio in 2020. It was also evidence that wild polioviruses had made their way to Malawi from Pakistan, one of only two countries on the planet where wild polio still circulates.

Four neighboring countries in East Africa will join the mass vaccination campaign — Zambia, Mozambique, and Tanzania initially, and in later rounds scheduled for May and June, Zimbabwe will also join the effort, said Modjirom Ndoutabe, polio coordinator in the World Health Organization’s Regional Office for Africa.

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The vaccination efforts in Zambia, Mozambique, and Tanzania are scheduled to start next week; each will conduct a four-day round. It’s estimated that about 9.4 million children will be vaccinated in this first round.

Borders in this part of the continent are porous, with considerable and regular movement of people and goods across them. That contributed to the decision to take a regional approach, as did a three-month delay in getting results from the testing of the paralyzed child. Polio has a head start, those planning the response understand.

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“We cannot know really the magnitude of the problem. Is this virus spreading already in those countries or not?” Ndoutabe told STAT from Brazzaville, in the Republic of the Congo, where he is based. “So adding Zimbabwe, it’s just to be sure that we can handle broadly the situation and not allow polioviruses to spread in the other countries.”

Janet Kayita, the WHO’s acting country representative for Malawi, said detailed work has been underway to plan the vaccination campaign, which will target all children under the age of 5, regardless of their previous vaccination status. In campaigns like these, vaccination teams go door to door, trying to ensure that over a very short period of time — four days in this case — all children receive a dose of oral polio vaccine.

The effort will be repeated again in April, May, and June.

“It’s huge. It’s huge. For Malawi alone, the under-5 population is … about 2.9 million,” Kayita said in an interview. “It’s a huge health system-wide effort by everybody over four days. Repeated four times. Four rounds. So it’s a massive, massive effort.”

Kayita said the confirmation of the case triggered a field investigation that involved interviewing the affected family, neighboring families, and chart reviews at nearby health centers to ensure that other cases have not been missed. No travel link between the affected family and Pakistan was found, meaning the child was infected by viruses that were circulating in Malawi.

“Thus far, we have not had any other confirmed cases. Of course, we also have samples continuing to come through the routine surveillance system. We haven’t picked up anything else,” Kayita said.

But polio is an insidious foe. It spreads easily from child to child, but doesn’t sicken most of them. Some will have minor, transient symptoms. However, about one out of every 200 children who are infected will be permanently paralyzed.

Other conditions or infections can cause paralysis, so polio is not always as easy to spot as one might think. Part of the work that has been underway, Kayita said, is aimed at raising awareness of the disease and its symptoms among health workers across Malawi, some of whom would never have seen a case of polio.

The response is being coordinated with the help of the partners in the Global Polio Eradication Initiative — the WHO, UNICEF (the UN Children’s Fund), the service club Rotary International, the Centers for Disease Control and Prevention, and the Bill and Melinda Gates Foundation.

In addition to looking for evidence among children of transmission of polioviruses, the country has begun conducting environmental surveillance — testing sewage samples for polio viruses. This type of surveillance, which is also used for Covid-19, is a routine part of polio surveillance in South Asia, but has not been done up until now in Malawi. Eleven surveillance sites have been established in four Malawian cities.

In normal times the country’s vaccination rates have been high — over 90% for polio, Kayita said. But the pandemic has hindered delivery of public health services the world over and Malawi is no exception. Kayita said that in the work done to map out next week’s campaign, it was seen that in some districts polio vaccination rates were below 80%.

“We missed a lot of children who have not been vaccinated against polio with routine immunization,” Ndoutabe said of the effect of the pandemic.

The residual damage of Tropical Storm Ana, which battered Malawi in January, has complicated planning for the mass vaccination campaign. Kayita noted that the flooding from the storm washed away roads and bridges in some parts of the country. It also in some places destroyed refrigerators used to store vaccines — the so-called cold chain that is a key requirement of vaccination programs.

Kayita said work has also been underway to alert the public to what is coming and why it is being done, in the hopes of ensuring parents cooperate with vaccination teams.

“We do have vaccine hesitancy. There are communities who are not easily accepting of vaccines,” she said. “This is why a key pillar of the response is massive efforts around social mobilization.”

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