This past summer saw one case of paralysis due to the polio virus. The case occurred in an Orthodox Jewish community in Rockland County. Polio had been eliminated in the U.S. and the last reported case was in 2013. Initial reports that the patient, who was unvaccinated, had been infected by contact with someone who had travelled out of the country, turned out to be incorrect. Genomic testing found that the case was caused by a vaccine-derived poliovirus. According to the CDC, the virus had been circulating locally for at least a year. Infection with poliovirus, an enterovirus that primarily infects the gastrointestinal tract, is symptomatic only about 25% of time, causing a flu-like illness. Depending on the virus type, 1% to 5% of patients will develop meningitis, an inflammation of the tissues that cover the brain and spinal cord. Even so, only about 0.5% to 0.05% of those who become infected will develop paralysis. Because of these numbers, experts believe that at least 100 members of that community were infected but asymptomatic. Genetically similar poliovirus has been detected in wastewater in Rockland and Orange Counties, as well as in NYC. This confirms that the virus has indeed been circulating in those communities and probably others for some time now.
So, if polio has been eliminated and the detected poliovirus is genetically the same as the virus used in vaccines, where did it come from? The CDC has confirmed that the virus did not come from out of the country. The answer lies in the vaccine type, of which there are two. Since 2000, the US has exclusively used the injectable poliovirus vaccine, or IPV. That vaccine contains only dead virus. Following vaccination, the vaccinated individual will shed the virus via urine and feces. In the IPV case, the individual will shed dead virus, which is harmless to others. However, the oral poliovirus vaccine, or OPV, uses an inactivated, or weakened poliovirus. The vaccinated individual will shed live virus, which in rare cases may regain its strength. This is one of the reasons the U.S. stopped using the OPV in 2000, however it is still used in many other countries. The CDC experts believe that someone in that Rockland community received the oral vaccine overseas and unwittingly brought the virus home with them. There is one other important difference between IPV and OPV. Both, after three doses, impart a life-long immunity that is very effective (99% for IPV, 95% for OPV) however, because OPV uses a live virus, there have been rare cases of vaccine-derived paralysis (one case of paralysis in one to three million vaccinations).
Currently, the CDC recommends one booster shot for adults who have had the three previous doses of IPV and who are at high risk of polio exposure. This includes people who are travelling to areas where polio is still endemic (Afghanistan and Pakistan), lab technicians who handle poliovirus samples, and healthcare workers and others caring for infected individuals. Those who administer the vaccine are not at risk. Finally, if you live or have close relatives who live in the Rockland County community in question, speak to your doctor about getting a booster shot.
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