SINGAPORE – On February 7, a five-month-old Indonesian girl who arrived in Singapore for urgent medical treatment was confirmed to be a case of vaccine-associated polio. This marks a concerning development in a disease that has been largely eradicated thanks to vaccination efforts.
The Ministry of Health (MOH) reported that the infant was evacuated from Indonesia on January 26, displaying symptoms of fever, muscle weakness, and paralysis in her legs. This case follows the global resurgence of polio in August 2024, when the disease was confirmed in Gaza after a 25-year absence.
Polio, once one of the most feared diseases in the 20th century, has seen its incidence drastically reduced since the introduction of vaccines by American physician Jonas Salk in the 1950s. In Singapore, no本土 cases of polio have been recorded since 1978. The last imported case, involving a two-year-old Nigerian girl, was in 2006.
Given the rarity of polio and its devastating impact, understanding its causes, symptoms, and preventive measures is crucial. Here’s a detailed look at the disease, its transmission, and how to safeguard against it.
What is Polio and How Does It Spread?
Polio, also known as poliomyelitis, is a viral infection caused by the poliovirus. First described in 1789 by British doctor Dr. Michael Underwood, it was formally recognized as a medical condition by German physician Jakob Heine in 1840. The disease spread worldwide by the mid-20th century, claiming the lives or paralyzing over half a million people每年.
While polio can affect individuals of all ages, it most commonly targets young children. Those who survive the disease often face lifelong physical challenges.
Highly contagious, polio can be transmitted from person to person. The primary mode of transmission is through the fecal-oral route, where the mouth of an uninfected person comes into contact with the feces of an infected individual. It can also be spread through contaminated water or food. Once in the human body, the poliovirus multiplies in the intestines and can invade the nervous system, leading to paralysis.
Symptoms of Polio
The early symptoms of polio can resemble those of the flu:
- Fever
- Fatigue
- Headache
- Vomiting
- Neck stiffness
- Pain in the limbs
According to the Ministry of Health’s HealthHub website, most patients experience mild symptoms or none at all. Severe symptoms, which can result in permanent paralysis, occur in a small percentage of cases.
Types of Polio
Wild Poliovirus: There are three strains of wild poliovirus—WPV1, WPV2, and WPV3. All can cause paralysis or death. However, due to the Global Polio Eradication Initiative’s vaccination efforts, WPV2 and WPV3 were eradicated in 2015 and 2019, respectively. WPV1 remains endemic only in Pakistan and Afghanistan, with global incidences declining from around 350,000 cases in 1988 to just six in 2021.
Vaccine-Associated Poliovirus: This is a rare complication from the oral polio vaccine (OPV). When administered, the weakened forms of the virus replicate in a patient’s intestines, producing immunity and excreted in faeces. In underimmunized communities with poor sanitation, these weakened viruses can circulate, mutate, and regain disease-causing abilities. Such cases are extraordinarily rare, occurring in approximately one in 2.7 million doses of OPV.
Prevention of Polio
While there is no cure for polio, the disease can be effectively prevented through vaccination. The World Health Organization (WHO) recommends vaccination as the primary method for protection. In Singapore, children receive five doses of the inactivated polio vaccine (IPV) under the National Childhood Immunization Schedule. The doses are administered at two months, four months, six months, 18 months, and between 10 and 11 years old.
Since 2021, Singapore has discontinued the use of the OPV, opting instead for IPV due to its safety profile. Despite theOPV’s cost-effectiveness and ease of administration, which make it the most widely used global vaccine, the risk of vaccine-associated polio remains a consideration.
Ensuring high vaccination rates and maintaining proper sanitation practices are essential in preventing the spread of polio, whether through wild poliovirus or vaccine-associated strains.
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