As war continues to devastate Gaza and its people, a concerning development has emerged: a variant of poliovirus has been detected in the region. This discovery, based on six sewage samples collected in late June from Khan Younis and Deir al Balah, highlights a potential threat to public health. While most poliovirus infections are asymptomatic, a significant minority can lead to paralysis, known as paralytic polio. Fortunately, no cases of paralytic polio have been reported in Gaza. However, the presence of the virus in wastewater is a cause for alarm.
Poliovirus has historically been categorized as ‘wild poliovirus,’ affecting both developed and developing nations, including Australia. The introduction of effective vaccines in the 1960s significantly reduced cases in countries with access to these medical advancements. The Global Polio Eradication Initiative, established in 1988, aimed to make vaccination more equitable, leading to a dramatic decrease in wild poliovirus cases. In 2023, only 12 cases of paralysis caused by wild poliovirus were reported, confined to Pakistan and Afghanistan.
However, as the prevalence of wild poliovirus declined, cases of vaccine-derived poliovirus (VDPV) causing paralysis increased. There are two types of polio vaccines: oral and injectable. The oral polio vaccine, composed of a weakened virus, does not cause disease but can still replicate within the body. VDPV emerges when individuals vaccinated with the oral polio vaccine excrete the vaccine virus in their stool, potentially spreading it to others. Over time, this excreted virus can mutate and become a circulating virus capable of causing paralysis in populations with low immunity. In 2023, 524 polio cases in 32 countries were attributed to VDPV.
The detected strain in Gaza’s wastewater is a type 2 VDPV. Achieving high vaccination coverage is crucial for eradicating both wild and vaccine-derived polio. Typically, this is measured as the percentage of children under five receiving at least four vaccine doses, ideally reaching 95 percent. While high vaccination coverage can be achieved through routine immunizations and targeted catch-up campaigns, it doesn’t always guarantee the elimination of the virus.
In the early 21st century, India and Nigeria had the highest polio case numbers globally. Despite successful immunization campaigns leading to high vaccine coverage rates in India by 2007, cases persisted in impoverished districts of western Uttar Pradesh. This persistence was linked to poor access to clean water and sanitation, factors that can hinder the effectiveness of the oral polio vaccine and facilitate virus transmission. A sanitation and hygiene project implemented in 2007 resulted in the last polio case in Uttar Pradesh occurring in 2010, ultimately leading to India’s eradication of polio in 2014.
Gaza’s last wild polio case was eradicated over 25 years ago. However, the re-emergence of VDPV in the region could be attributed to a combination of poor hygiene, sanitation, and reduced vaccine coverage, similar to the situation in Uttar Pradesh. Polio vaccination coverage in the Palestinian territories was 99 percent in 2022, but dropped to 89 percent by the end of 2023. As data is not separated by territory, coverage in Gaza may be even lower.
Similar strains of poliovirus were detected in wastewater samples from Jerusalem, London, and New York in early 2022. These cities have areas with high concentrations of Ultra-Orthodox Jews, who may have lower vaccination rates compared to the general population. In Rockland County, New York, an unimmunized young Orthodox Jewish man contracted polio, marking the first case of locally transmitted polio in the United States in 30 years.
The oral vaccine used in Gaza hasn’t contained type 2 since 2016, suggesting the source of the virus is external. In 2023, most outbreaks of type 2 VDPV occurred in the Democratic Republic of Congo, Yemen, Nigeria, Sudan, and Somalia. A case was also reported in Egypt, which borders Gaza. While Egypt could be the source of the virus, further investigation is needed. Israel, which shares a border with Gaza, hasn’t detected poliovirus in wastewater since 2022, making it an unlikely source.
The detection of poliovirus in Gaza highlights several crucial points. First, the virus can cross borders, emphasizing the importance of maintaining high vaccination rates globally. Second, containing the virus within Gaza is paramount. UNICEF and partners are preparing a vaccination campaign focusing on young children. Third, continuous wastewater surveillance for polio is crucial for early detection and intervention before symptomatic cases occur. Fourth, the situation underscores the urgent need to cease hostilities in Gaza and provide unrestricted access for aid agencies to improve sanitation, clean water, and healthcare services. This is a global health priority.
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