By Michael Gwarisa
In November 2023, Zimbabwe’s environmental surveillance system picked a vaccine-derived poliovirus type 2 (cVDPV) strain, circulating in the sewage system in Harare’s high density suburbs namely Budiriro, Mbare and Mufakose. A similar variant was detected in a 10-year-old child from Sanyati District in Mashonaland, West Province. The child has since developed paralysis following the Polio infection.
Two other children in Mbare have had the same strain detected in them despite the absence of paralysis developing in either of them. Over the past few days, the Ministry of Health and Child Care (MoHCC) launched an emergency polio vaccination blitz in response to the new strain. The vaccination campaign is targeting not less than 4.2 million children aged 10 years and younger following a Ministry of Health’s risk analysis which identified children within that age range as high risk group for the circulating mutated virus. The vaccination campaign kicked off on February 20, ending March 1, 2024.
However, of great concern amongst members of the public is the safety and effectiveness of the vaccination exercise in the midst of a circulating vaccine derived variant. One concerned parent who wrote to this publication said, “I am at crossroads. My daughter is supposed to receive that vaccine. Should I let her or it’s risky?” He is justified to have such fears and is certainly not the only parent in that situation.
Polio is the short name for poliomyelitis, a highly infectious disease caused by the poliovirus. There are three wild types of polioviruses, types 1, 2, and 3, and only two countries where the wild poliovirus type 1 is still endemic: Afghanistan and Pakistan. In 1962, an oral polio vaccine (OPV) was developed by researcher Albert Sabin, using an attenuated, or weakened live polio virus. As his vaccine was easier to administer, it greatly facilitated distribution.
When vaccines are developed, safety and efficacy are the biggest priority. In order to guarantee safety and effectiveness of vaccines, every country has been mandated by the World Health Organisation (WHO) to establish a NITAG, which is an evidence-based National Immunization Technical Advisory Group.
Zimbabwe has its own NITAG known as the Zimbabwe National Immunisation Technical Advisory Group (ZIMNITAG). Dr Nhamo Gona, the ZIMNITAG Chairperson and chair for the National Certification Committee for Polio Eradication told Journalists during a Media Engagement on the obtaining Polio situation in the country that the NITAG won’t approve use of any vaccine if they are not certain of its safety and effectiveness.
This is a multidisciplinary committee. Whatever we do is based on evidence. Every country was advised by WHO to have a NITAG because the immunization landscape is very complicated. People have to understand different factors in terms of vaccine safety, vaccine effectiveness, immunization characteristics, and the disease burden, and also we look at the programmatic issues and health economics before we decide or to make a recommendation on using the vaccine,” said Dr Gona.
Zimbabwe’s NITAG is the oldest on the African continent and works with in technical working groups. Each one is given a certain area to look at and thorough research is done. A NITAG is composed of scientists including people from the laboratory. These are virologists, people with public health expertise, immunologists, paediatricians as well as physicians. These join the NITAG on a voluntary basis in order to maintain professionalism and safeguard the interest of the NITAG without eternal interference.
Dr Sadiq Umar, the Global Polio Eradication Initiative Coordinator in the World Health Organization (WHO) said the polio vaccine that is being administered in Zimbabwe, emanates from a family of vaccines known as live-attenuated vaccines, whereby the primary cause of the diseases is inactivated somehow to make it less pathogenic.
“When we say attenuated, we mean you take the virus, it passes through some laboratory activities to reduce its capacity to cause a frank disease (that means disease with signs and symptoms) so that it will mimic an infection with the true virus but it will not be strong enough so that the person will be coming down with paralysis. In other words, it is the same organism that causes Polio, we wanted it to go through the natural processes in the body so that our body through the way it is structured, it will produce protection naturally against the disease,” said Dr Umar.
The live-attenuated vaccine is a vaccine that was produced using the poliovirus which was reduced its capacity to cause frank disease. Polio infects its host through ingestion hence the polio vaccine is administered orally.
“These vaccines that are produced Live-attenuated are administered orally that means when we take them orally, whether its oral Cholera Vaccines, oral Typhoid or Polio vaccines, the primary causing or diseases virus itself goes to our small intestines and multiplies. The vaccines multiplies there in the small intestines so that it reproduces itself more. In the process, our body will sense it and then it will start producing antibodies and attack the foreign body. When the real danger or live polio attacks the body, the body will also recognise the foreign body and attack the disease.”
He added that about 90% of people who get infected with Polio will not exhibit any symptom or sign. They feel normal and around 9.9% will show symptoms and signs and these symptoms and signs can present as stomach pain, fever, general body pains, body pains, anorexia, vomiting and even diarrhea. These can be treated just like any normal diseases. However, 1% of children who get Polio develop paralysis, which is the severe form of Polio and cannot be treated or reversed.
What is Vaccine-Derived?
When an attenuated vaccine is administered, it settles in the small intestines where it interacts with the normal micro-organisms in the gut. As they interact, they may exchange genetic information prompting the attenuated virus to start gathering some momentum by getting lessons from genetic material from other normal organisms that are in the gut.
“It is then that the vaccine alters its capacity to cause disease. Instead of protecting against infection, the vaccine starts fighting and causing symptoms. Any virus that changes or mutates its genetic component and becomes virulent, we call it Vaccine-derived,”Dr Umar said.
Severity and Risk Factors of the Vaccine Derived Poliovirus Circulating in Zimbabwe
There are three serotypes of wild poliovirus: type 1, type 2, and type 3 each with a slightly different capsid protein. There is the Wild Type of Polio virus and this according to Dr Umar, is the most severe form of Polio. However, Zimbabwe has not yet recorded the Wild Polio type as yet.
“The vaccine-derived virus that we are experiencing in Zimbabwe is the least severe form of the disease. The Wild Type of Polio are the most dangerous that is why when we had infections of the wild type in Malawi and Mozambique, everything stood, everything stopped because it is the worst scenario you can think of. It causes more paralysis than the vaccine derived strain by several hundred folds.”
Under Wild Polioviruses there are Type 1 and Type 2 and 3. Under Vaccine-Derived Polio viruses, there are also Type 1, 2, and 3. Any of the types can change its configuration.
Dr Umar added that the vaccine derived doesn’t occur in areas that are well protected or where immunisation coverage is high.
“If you see Vaccine- derived virus occurring, it is in areas where there are gaps in the immunisation systems or where there are gaps of many children that get vaccinated or have not completed their calendar for vaccination. If you may recall, vaccine-derived viruses were picked in New York, United States of America and in London, United Kingdom. However, because immunisation coverage is high there, you didn’t hear it spreading and also their Water Sanitation and Hygiene (WASH) is also very high there,” he said.
Other risk factors for Polio in Africa include migration due to war, conflict, natural disasters, low quality of responses, poor Water Sanitation and Hygiene (WASH) services among others.
Origins of the Vaccine Derived Polio Virus Circulating in Zimbabwe
In March 2016, the Strategic Global of Experts agreed that the trivalent (3OPV) be removed from being administered during routine immunization activities following challenges with the vaccines. To date, there is no country in the world that is using 3OPV vaccine. It was associated with two other vaccines, one of them being RPV vaccine that is used for protecting children during routine immunization. This one doesn’t work in outbreaks. After the removal of 3OPV, the monovalent oral polio vaccine type 2 (mOPV2) was introduced to respond to outbreaks. However, this vaccine exhibited high propensity of changing its genetic component and become more aggressive. The mOPV2 was withdrawn following this anomaly and replaced with the novel oral polio vaccine (nOPV2).
“No country uses mOPV2, no country uses 3OPV, these have been withdrawn and we are left with the nOPV, n stands for novel,” said Dr Umar.
However, even though the mutating mOPV2 was withdrawn, a number of countries on the African continent had already used it. Due to depressed vaccination levels following the withdrawal of 3OPV in 201, and also due to low vaccination coverage at the back COID-19 induced knockdowns, the vaccine derived strain mutated and spread into unsuspecting populations. The mOPV2 strain is circulating on the continent largely due to human travel.
Prevalence of Vaccine-Derived Poliovirus
There about 28 African countries that have reported circulation of the vaccine-derived poliovirus. These include, Algeria, Benin, Botswana, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Côte d’Ivoire, Congo, Democratic Republic of the Congo, Ghana, Guinea, Kenya, Madagascar, Malawi, Mali, Mauritania, Mozambique, Niger, Nigeria, Tanzania, Togo, Zambia and Zimbabwe.
“In Zimbabwe, we have never used mOPV2 but Zambia have used, Mozambique have used and any other Africa countries. Therefore anyone from these countries could have come here and passed stool that carried the poliovirus and went into the sewer system of Zimbabwe or Vice-versa. A Zimbabwean might have visited any of the countries and came back, passed stool and it was picked in the sewage system,” Dr Umar noted.
Won’t the nOPV2 mutate and cause Vaccine-Derived Polio infections in the future?
The nOPV2 is currently in the wider use roll-out phase under WHO Emergency Use Listing (EUL) for the control of type 2 circulating vaccine-derived poliovirus (cVDPV2) outbreaks, in line with the Strategic Advisory Group of Experts on Immunization (SAGE) guidance.
