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New polio strain caused by vaccines, says expert


By Tonny Abet

Just 12 months after being declared polio-free, the Ministry of Health has announced a fresh outbreak of the crippling and potentially fatal infectious disease.

The World Health Organisation Independent Africa Regional Certification Commission for Polio Eradication, on August 25, 2020, officially declared Uganda and the African region free of wild polio virus. 

President Museveni has also repeatedly highlighted the eradication of polio as one of the major achievements of his government.

But the Ministry of Health in an August 12 press statement said Uganda, like other countries in the continent, is experiencing an outbreak of a strain of polio dubbed “vaccine-derived polio virus type 2 (cVDPV2).”

The Ministry warned that up to 4.6 million children under five years are at high risk of contracting the virus, saying there is an urgent need to do mass polio vaccination within 120 days to interrupt the transmission. 

Prof Pontiano Kaleebu, the director of Uganda Virus Research Institute (UVRI), said the virus was discovered by their scientists a few weeks ago during a routine surveillance.


The scientists picked samples from sewage plants of Bugolobi and Lubigi in Kampala in June for laboratory analysis, according to Prof Kaleebu.

The polio virus can live in an infected person’s feces for many weeks and this can contaminate food and water in unsanitary conditions.

“Our team here at UVRI does surveillance with the aim of eliminating polio globally. The particular work we do is to look for any polio in the environment,” Prof Kaleebu said.

“We have done well in the country; so far we don’t see cases of polio. But we also check in the environment, especially in the sewage like Bugolobi and Lubigi where our scientists picked samples and cultured,” he added.
Culturing is a method of multiplying infectious agents by letting them reproduce in controlled laboratory conditions. The infectious agents can then be used for disease diagnosis or other assessments. “A few weeks ago, when they were culturing, they found that some samples had type 2 polio. 

They had to send the samples to South Africa [laboratory] for sequencing from where it was confirmed that it is vaccine-derived strain [of polio] found in the sewage,” Prof Kaleebu said.

He added that the new virus behaves like wild polio which is considered highly infectious. “No person has been reported with it so far [in the country],” the expert added.

Major outbreak anticipated
However, Dr Henry Mwebesa, the Director-General of health services, in the August 12 statement, said “identification of a cVDPV2 from the environment in Uganda confirms that there are persons in the Kampala area shedding the disease.He said as high as 959 cases of cVDPV2 have been confirmed globally last year and that about 20 countries in the continent have cases of the virus.

“In the context of low immunity against type 2 [polio virus], cases already being reported from the neighboring countries and weak surveillance systems; a large scale polio outbreak with a potential for spreading fast is eminent,” Dr Mwebesa said.

There is no cure for Polio, but vaccines, which are given multiple times can protect a child for life, according to WHO.

Origin of the new strain

Polio disease is caused by a group of three unrelated viruses called wild polio type 1, type 2 and type 3.
Prof Kaleebu said the vaccine-derived polio virus type 2 could have emerged because of changes in the genetic materials of the existing polio viruses.

“This could be some mutations resulting from the vaccine we use [against polio] and that has always been a concern [to scientists]. The vaccines we use have attenuated virus and the virus could mutate and lead to this [new strain of polio virus],” he said.

The expert revealed that in some countries excluding Uganda, the use of attenuated vaccines have been stopped and they have moved to killed vaccines because the virus can’t mutate.  
An attenuated virus is a live virus that has been made weak so as not to cause disease. But the weakened virus, once injected into the body, can stimulate an immune response against the targeted disease.

Dr Mwebesa said the sequencing in South Africa laboratory found that the strain has 28 changes, “which means that it’s likely been circulating for over two years in Uganda.

He said that in communities with low immunisation rates, the virus is spread from one unvaccinated child to another over a long period of time, usually between 12-18 months.

“[As the virus spreads], it can mutate and take on a form that can cause paralysis just like the wild poliovirus. This mutated poliovirus can then spread in communities, leading to cVDPVs,” he said.

The country has been grappling with low coverage of polio vaccines and that vaccine being used in the country has a relatively low efficacy of 64 per cent.

For instance, the statistics from the Ministry indicate that in 2016, the polio vaccine coverage was at 44 per cent, 2017 (70 per cent), 2018 (84 per cent) and 2019 (88 per cent).

Dr Mwebesa said owing to the low coverage of polio vaccine, as high as “4.6 million children under 5 years are susceptible to paralytic infection of type 2 polio virus.”

Through mass polio campaigns, polio virus types 2 and 3 had been eradicated globally, according to Dr Mwebesa. Similarly, type 1 has also been eradicated in Africa.

The Director-General also revealed that the country stopped vaccinating children against type 2 polio in 2016 after the world was declared free of it. Only the vaccines for type 1 and 3 are in use in the country.

Gaps that must be filled
“Such undetected transmission suggests that there are gaps in the national Polio surveillance sensitivity that need to be identified and corrected urgently,” Dr Mwebesa said.  

The last indigenous wild polio virus in Uganda was identified in 1997 and Uganda was certified free of all polio viruses in 2006.

Dr Mwebesa said that as a result of continued threats of importation of the viruses, in 2009 and 2010, Mayuge and Bugiri reported cases of polio which resulted in repeated 23 cycles of polio vaccinations.

The Director-General said the country is facing big threats of further importation of the virus from South Sudan, Ethiopia, Somalia, and Yemen due to poorly controlled cross-border movements.  

The Ministry of Health is also concerned about the poor hygiene in the country that can spur the spread of  polio virus.

“Eight million Ugandans lack access to safe water and 27 million do not have access to improved sanitation facilities,” Dr Mwebesa said.

The Ministry has outlined mass vaccination against polio, restricting travellers from high-risk countries and improving surveillance of the disease within the country as quick actions that will be undertaken to interrupt transmission.

Mr Emmanuel Ainebyoona, the spokesperson for the Ministry, said plans are underway to implement the plans.
“We intend to carry out vaccination in October and December. Parents who have children who are below five years are taken for vaccination,” he said.

According to Dr Mwebesa, there will be screening and provision of polio vaccine to children under five years without card documented polio vaccination.

“The Ministry of Local Government, district local governments and urban authorities ensure no single child misses out on routine vaccination services… Districts with international borders revitalize cross-border collaborations aimed at enhancing the quality of polio surveillance,” he said.

Prof Kaleebu said due to mutations in the virus, there is a need for a quick study to determine whether the vaccine at hand will still be effective against it. 

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