By Treezer Michelle Atieno
Kenya has faced a polio outbreak in 2024, with six polioviruses detected so far. The outbreak is caused by circulating vaccine-derived poliovirus type 2 (cVDPV2), which is highly transmissible and has low vaccination coverage. Treezer interviewed Dr. Christine Chege to find out more about polio and Kenya’s efforts in dealing with the outbreaks. Dr. Chege is a pediatrician and pediatric infectious disease specialist. She serves as the chair of the Department of Pediatrics at Kenyatta University School of Medicine and a member of the Kenya Pediatric Association focusing on advocacy for child health and survival.
Q: What is polio, and why do we talk about “polio eradication”?
Dr. Chege: Polio, or poliomyelitis, is a viral disease that can cause irreversible paralysis. It is targeted for eradication because it does not have an animal reservoir; it only spreads between humans. This characteristic makes it easier to eradicate compared to other diseases. Globally, there are three serotypes of the poliovirus, and Types 2 and 3 have already been eradicated. This leaves us with Type 1. However, Kenya has recently recorded Vaccine-Derived Poliovirus (VDPV). Eradicating the virus requires effective vaccination campaigns, making vaccines accessible, and spreading accurate information to ensure high immunization coverage.
Q: Before we get to Vaccine-Derived Poliovirus (VDPV), you have mentioned three different types of poliovirus. How are they different?
Dr. Chege: Poliovirus Type 1 (WPV1) is the most severe and widespread strain, responsible for the majority of polio outbreaks globally. It remains the only strain still in circulation. WPV1 can cause severe paralytic polio more frequently than the other types, with symptoms including fever, fatigue, headache, vomiting, neck stiffness, limb pain, and paralysis in severe cases. This type continues to pose a significant health threat, especially in areas with low vaccination coverage. As I previously mentioned, poliovirus Types 2 and 3 have both been eradicated globally. Although WPV2 no longer circulates, vaccine-derived strains (VDPV2) can still cause outbreaks in areas with poor immunization coverage, presenting symptoms similar to WPV1 but typically less severe. Type 3 was less severe than Type 1 but still contributed to outbreaks before its eradication. Symptoms for both Type 2 and Type 3 included fever, fatigue, headache, and, in rare cases, paralysis, though generally less frequent or severe than in WPV1 cases.
Q: What is Vaccine-Derived Poliovirus (VDPV), and how does it occur?
Dr. Chege: Vaccine-derived poliovirus (VDPV) occurs when the weakened virus in the Oral Polio Vaccine (OPV) mutates over time. In areas with poor sanitation, such as open sewers, children who have received the OPV excrete the vaccine virus into the environment. This virus can undergo mutations and revert to a virulent form. If other children who are under-vaccinated or unvaccinated come into contact with contaminated water or food, they are at risk of contracting this mutated strain. This is particularly the case for Type 2 poliovirus, which is no longer part of the OPV but remains a threat in such environments.
Q: Are there any responses or interventions to the risks associated with OPV?
Dr. Chege: Yes. The World Health Organization (WHO) has recognized the risks associated with the Oral Polio Vaccine (OPV), particularly with the Type 2 strain, which was responsible for most cases of Vaccine-Associated Paralytic Polio (VAPP). In response, they have transitioned to a safer alternative, the Injectable Polio Vaccine (IPV). The IPV does not contain live virus, so it eliminates the risk of vaccine-derived poliovirus. Initially, IPV was introduced while gradually withdrawing the OPV. Today, the OPV being used is bivalent, containing only Types 1 and 3. The ultimate goal is to replace OPV entirely with IPV, ensuring that no live poliovirus is used in vaccines.
Q: What has been Kenya’s recent experience with polio, especially circulating Vaccine-Derived Poliovirus Type 2 (cVDPV2)?
Dr. Chege: This year, we experienced an outbreak of circulating Vaccine-Derived Poliovirus Type 2 (cVDPV2). Five cases were confirmed, four children from Kakuma Refugee Camp in Turkana County and one positive environmental surveillance sample from Kamukunji Sub-County in Nairobi. The Ministry of Health responded with a nationwide vaccination campaign targeting over 3.8 million children under five across nine high-risk counties. These include Nairobi, Busia, Bungoma, Turkana, Trans Nzoia, West Pokot, Kiambu, Machakos, and Kajiado. We achieved the 90% vaccination target for all these counties.
Q: What are the key challenges Kenya faces in eradicating polio?
Dr. Chege: One of the biggest challenges is low immunization coverage in some areas. For effective eradication, at least 90% of the population needs to be vaccinated. Unfortunately, some counties in Kenya have coverage rates as low as 50%. This is especially true in northern regions and urban slums where access to healthcare is limited, and sanitation is poor. These conditions increase the risk of VDPV outbreaks.
Another challenge is vaccine hesitancy, often driven by misinformation. There are concerns raised by communities about vaccine safety, which slows down immunization efforts. Ensuring accurate information is available to the public and maintaining confidence in vaccines are crucial steps toward eradicating polio.
Q: How is polio detected in Kenya, and what measures are in place to monitor its spread?
Dr. Chege: Polio is detected through two main methods: environmental surveillance and clinical detection. Environmental surveillance involves testing sewage samples from strategic locations across the country. When poliovirus is detected in these samples, it indicates that unvaccinated or under-vaccinated children in the area are at risk.
Clinical detection occurs when a child presents with acute flaccid paralysis, a typical sign of polio. In Kenya, all sub-counties are assigned targets for monitoring acute flaccid paralysis in children under 15 years old. Samples are sent to the Kenya Medical Research Institute (KEMRI) for testing, and weekly monitoring helps track any new cases.
Q: How does Kenya ensure the success of polio vaccination campaigns, particularly in high-risk areas?
Dr. Chege: The success of vaccination campaigns relies on close collaboration between the Ministry of Health, WHO, UNICEF, the Kenya Pediatric Association, and other partners. For example, the recent vaccination campaign was successful because it targeted specific high-risk areas and expanded the age group in certain counties to include children up to 10 years old. This was necessary in areas like Busia, Bungoma, and West Pokot due to higher risks of transmission.
Community health promoters play a vital role in these campaigns, administering the oral polio vaccine (OPV) and ensuring that vaccines are stored correctly in carrier boxes with ice packs. The campaigns typically involve door-to-door visits, and vaccination posts are set up in public places like markets and churches to reach as many children as possible.
Q: What role does public confidence play in the success of polio eradication efforts, and how can misinformation be tackled?
Dr. Chege: Public confidence is critical. If people believe in the safety and effectiveness of vaccines, they are more likely to vaccinate their children, which brings us closer to eradicating polio. Unfortunately, misinformation, often spread through social media, can erode that confidence. For example, there were recent concerns about vaccine safety in Kenya, but thorough investigations showed no direct link between the vaccine and reported adverse events. These incidents were coincidental.
To tackle misinformation, all stakeholders, including health workers and the media, must collaborate to provide accurate information to the public. The media plays a key role in this, as responsible reporting can prevent the spread of false claims and ensure that the public gets the right facts.
Q: What more needs to be done to finally eradicate polio in Kenya?
Dr. Chege: Kenya is on the path to eradicating polio, but there are still a few key gaps. First, we need to improve accessibility to vaccines. This means setting up mobile clinics and bringing vaccination services directly to underserved communities. Second, we need to strengthen public education to create demand for vaccines and build trust. If we can achieve 95% vaccination coverage, we can stop reporting polio cases and move on to other pressing public health issues.
Q: Are there any final thoughts you’d like to share?
Dr. Chege: Ultimately, polio eradication does not require extraordinary resources. The vaccines are available, and the infrastructure is in place. What we need is public confidence and accessibility to immunization services. Once these challenges are addressed, Kenya will be on its way to eradicating polio, just like smallpox was eradicated.
