Polio is a disease that the World Health Organization is seeking to eradicate worldwide. Today, wild polio cases occur only in Afghanistan and Pakistan. The success of this eradication work is due to the availability of two very effective vaccines. These vaccines work by causing the body to generate an immune response against the poliovirus. But the vaccines are not perfect, and we currently have poliovirus in wastewater in Britain, Israel, and the United States.
There are two types of polio vaccine in widespread use, an oral vaccine made from a weakened poliovirus (developed by Salk and Sabin) and an inactivated (dead) polio vaccine given by injection. Two injections of the inactivated polio vaccine provide immunity to about 90 percent of individuals (99 percent with three injections). The oral vaccine is easier to administer and more individually effective, and three administrations protect 95 percent of the population. But each of these vaccines has a small weakness.
The inactivated polio vaccine protects the individual but is not as effective at preventing transmission (apparently, people can still get asymptomatic polio and pass it on). The oral poliovirus vaccine in a small number of cases (one in 750,000) reverts to a virulent form and can then be passed on to others, leading to what is called vaccine-derived poliovirus. This slight but real possibility has led most developed countries to use the injected, inactivated polio vaccine. In other countries, the oral vaccine is still used because of its ease of administration.
This summer, vaccine-derived poliovirus resulted in polio and paralysis in an unvaccinated individual in New York who had not recently travelled abroad. Since polio causes paralysis in only one in 2,000 individuals, this suggested widespread virus circulation and wastewater testing confirmed the virus was circulating in the community. Similar testing showed the same in London and Jerusalem. Public health agencies are increasing efforts to vaccinate children and unvaccinated adults in all three cities to nip this outbreak as quickly as possible.
Currently under testing is a new oral vaccine genetically engineered not to become harmful. Given emergency WHO approval, this vaccine has been used in about 100 million people with no signs of vaccine-derived poliovirus. With this vaccine wild and vaccine-induced polio could become a thing of the past, as is the case with smallpox. But even thanks to the current vaccines, we rarely worry about polio in Canada.
For COVID-19, we have six approved vaccines that use various techniques to develop an immune response to the spike protein that SARS-Cov-2 (the virus that causes COVID) uses to get into our cells, making us sick. Two effective vaccines use a new mRNA procedure; two are based on a viral vector; one is based on a plant-based virus-like particle; the sixth uses part of the spike protein (like what is used with polio vaccines). If you are uncomfortable with the new mRNA vaccine, talk to your doctor about the other approved vaccines, but get vaccinated! Doing so protects us from the worst effects of COVID and reduces its transmission. And in this time of thanksgiving, thank our Lord for the vaccines developed to help us fight polio, this pandemic, and other diseases.
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