Detection of Poliovirus in Gaza Sewage Samples July 23

• Mutated strains of type 2 poliovirus were discovered in six sewage samples collected from two environmental monitoring sites in Khan Younis and Deir al-Balah. Genomic analysis of these poliovirus isolates indicated that these strains are closely related genetically to each other and to the mutated poliovirus strain that circulated in Egypt during the latter half of 2023. The last detection of related mutated strains in Egypt was from samples collected in December 2023. Based on the genetic variations in the isolates, it is likely that the mutated virus was introduced to Gaza in early September 2023. It is important to note that, at this time, the virus has only been isolated from the environment, and no associated paralysis cases have been detected.
• The oral poliovirus vaccine (OPV), which has nearly eradicated wild poliovirus, provides superior intestinal immunity where poliovirus multiplies. However, the vaccine virus is also excreted in feces. In communities with poor sanitation, this can lead to person-to-person transmission, effectively protecting the community. 
• Nonetheless, in communities with low vaccination rates, the virus can mutate as it spreads from one unvaccinated child to another over 12-18 months, potentially causing paralysis similar to wild poliovirus. This mutated virus can then spread among unvaccinated children in the same communities, leading to vaccine-derived poliovirus (VDPV) cases. 

• Type 2 vaccine-derived poliovirus (VDPV2) was isolated from six environmental (sewage) samples in Gaza, collected from two distinct sites in the southern city of Khan Younis and Deir al-Balah in the north, as confirmed by the World Health Organization (WHO) on Friday.
• The Global Polio Eradication Initiative (GPEI), hosted by WHO, stated in a press release that the mutated virus strains discovered in all six sewage samples collected in late June are genetically related.
• GPEI's statement emphasized that "it is important to note that the virus has only been isolated from the environment at this time; no associated paralysis cases have been detected." However, the statement also warned that "WHO considers there is a significant risk of spread within Gaza and internationally, particularly given the impact of the current situation on public health services."

Poliovirus types

• Historically, poliovirus cases were primarily caused by "wild poliovirus." For centuries, wild poliovirus affected both poor and wealthy countries, including Australia. Effective vaccines introduced in the 1960s led to a significant decline in cases in subsequent decades among countries that could afford the vaccines.
• The launch of the Global Polio Eradication Initiative in 1988 aimed to achieve more equitable vaccination coverage. In 2023, only 12 cases of paralysis due to wild poliovirus were reported, confined to two countries: Pakistan and Afghanistan.
• However, as wild poliovirus cases declined, there was an increase in cases of vaccine-derived poliovirus.
• There are two types of polio vaccines: the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV), the latter being used in Australia. OPV relies on a weakened virus that does not cause illness but can replicate. Vaccine-derived poliovirus arises when individuals vaccinated with OPV excrete the vaccine virus in their feces, and it spreads to others.
• Over time, it may mutate into a virus that causes paralysis in populations with low immunity levels. In 2023, there were 524 cases of vaccine-derived poliovirus paralysis across 32 countries.
• It is this type of vaccine-derived virus—type 2—that was detected in Gaza's sewage.

• The World Health Organization has heightened alert status due to the detection of poliovirus in sewage samples in Gaza.
• Public Health Risk Assessment and Measures
• The Ministry of Health is currently conducting a risk assessment, including evaluating surveillance sensitivity for detecting acute flaccid paralysis (AFP) and environmental surveillance. Immunization levels are being assessed more clearly at the subnational level.
• ​WHO, UNICEF, and the United Nations Relief and Works Agency for Palestine Refugees (UNRWA) continue to work with all health authorities on the ground as part of urgent efforts to mitigate the impact of the current crisis on public health in Gaza. The ongoing crisis poses a significant challenge to full disease surveillance and vaccination services.
• Routine vaccination rates in the occupied Palestinian territories were optimal before the conflict began in October 2023. Polio vaccination coverage (POL3), primarily achieved through routine immunization, was estimated at 99% in 2022. This rate declined to 89% in 2023, according to the latest estimates from WHO and UNICEF. 
• Currently, only 16 out of 36 hospitals are partially functional, and 45 out of 105 primary healthcare centers are operational. The combined impact of the health system, insecurity, lack of access, population displacement, and medical supply shortages, along with deteriorating water quality and poor sanitation, has contributed to the decline in routine immunization rates and increased the risk of vaccine-preventable diseases, including polio.
• WHO considers there is a high risk of this strain spreading within Gaza and internationally, given the current impact on public health services.

Symptoms and Risks

• Polio is a highly contagious viral disease that invades the nervous system and can cause total paralysis within hours. The virus spreads mainly through person-to-person contact, primarily via the fecal-oral route, and less commonly through a common vehicle (e.g., contaminated water or food). It multiplies in the intestine. Initial symptoms include fever, fatigue, headache, vomiting, neck stiffness, and limb pain. One in 200 infections leads to irreversible paralysis (usually of the legs), and 5-10% of those paralyzed die when their breathing muscles become immobilized.
• Polio primarily affects children under the age of five but can infect any unvaccinated person, regardless of age.
• There is no cure for polio; it can only be prevented through vaccination. The polio vaccine, given multiple times, can protect a child for life. Two vaccines are available: the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV), both effective and safe. They are administered in various combinations worldwide, depending on local epidemiological conditions and programs to ensure optimal protection.

Treatment

• There is no cure for polio; it can only be prevented through vaccination. The polio vaccine, given multiple times, can provide lifelong protection against the disease. Since the launch of the Global Polio Eradication Initiative in 1988, more than 20 million people who would otherwise have been paralyzed are able to walk today. The systematic distribution of vitamin A during polio immunization activities has also prevented approximately 1.5 million childhood deaths.
• Available treatments for polio focus on alleviating symptoms. Heat and physical therapy can stimulate muscles, and antispasmodic drugs can relax affected muscles. These measures can improve mobility but cannot reverse permanent paralysis caused by polio.
• Vaccination is crucial in combating polio. Failure to implement effective strategies leads to continued virus transmission. Persistent transmission of wild poliovirus continues to cause cases in border areas of Afghanistan and Pakistan. Failure to eradicate polio in these last remaining areas could result in as many as 200,000 new cases annually worldwide within ten years. Therefore, it is essential to ensure the complete eradication of polio once and for all.

CDC Activities

•  Create a national registry that includes all facilities containing poliovirus.
•  Regularly update the registry to maintain accurate information.

•  Provide accurate annual updates to the RCC on the status of the national registry of facilities containing poliovirus.

• Create national emergency plans to deal with any cases of poliovirus release.
• Ensure rapid and effective response in the event of any virus leakage.

•  Oversee the destruction or deactivation of non-essential poliovirus materials.

• Prioritize IPV: Public health efforts should focus on increasing coverage of the inactivated polio vaccine (IPV), which is effective in preventing polio without the risk of vaccine-derived poliovirus. Ensuring high IPV coverage can help achieve community immunity and prevent outbreaks.

• Target Specific Areas: Gaps in immunization coverage may exist; targeted campaigns should be implemented. This includes ensuring unvaccinated or incompletely vaccinated individuals receive the full polio vaccination series.

• Increase Surveillance: Strengthen surveillance systems to effectively detect and track polio cases. This includes tracking immunization coverage and monitoring any new virus cases in the community.
• Rapid Response: Develop and implement rapid response strategies to address any potential polio cases or outbreaks. Quick action is essential to prevent virus spread and minimize the risk of paralysis cases.

• Awareness Campaigns: Increase public awareness about the importance of completing the polio vaccination series and the benefits of IPV. Public education campaigns can help address vaccine hesitancy and ensure higher vaccination rates.

• Collaborative Efforts: Work closely with local health authorities and healthcare providers to ensure effective vaccination efforts and that any polio cases are reported and managed according to public health guidelines.
• By concentrating on these areas, public health practices can reduce the risk of polio outbreaks and ensure communities are protected from this potentially devastating disease.

• World Health Organization (WHO)
• Centers for Disease Control and Prevention (CDC)
• Global Polio Eradication Initiative – WHO