Reported by Politico earlier today, a case of polio has been diagnosed in Rockland County (a NYC suburb), according to the New York State Department of Health and the CDC.
From the article: “The case announced Thursday involves a revertant polio Sabin type 2 virus, which health officials said is “indicative of a transmission chain from an individual who received the oral polio vaccine.” That vaccine type is no longer used in the U.S., which has administered the inactivated polio vaccine since 2000, suggesting that it may have originated outside the country. According to the CDC, the last time that happened was in 1993.”
The NY state health commissioner is strongly recommending that unvaccinated people get vaccinated or boosted with the FDA-approved inactivated virus vaccine as soon as possible.
What is a “revertant polio Sabin type 2 virus”? And what’s different about the current inactivated vaccine? It’s helpful to consider three main types of poliovirus and vaccine:
WPV = wild poliovirus: the original virus, before any vaccines existed. (Polio occurs naturally only in humans)
OPV = oral polio virus: a weakened version of WPV used for the first oral vaccine
IPV = inactivated polio vaccine (an injection containing an inactivated version of WPV, incapable of causing the disease but still effective in stimulating immune protection)
In August 1960 the oral (OPV) vaccine was licensed in the US. As a “live” vaccine, it contained a weakened form of the actual disease-causing virus. Using this weakened germ stimulated the immune system to fight natural polio (WPV), and was much safer than getting the disease.
The oral “Sabin” vaccine, named after its developer, was usually dropped on a sugar cube for dosing, so it was inexpensive and easy to take. Also because it was swallowed, it inactivated the polio virus in the human gut, which is where it replicates (and can be passed on in human waste).
OPV was incredibly effective in reducing and even eradicating natural polio.
However, one of the risks was that OPV contained the virus. Although it was in a weakened form, it could still mutate into a stronger or more virulent strain. This happens when someone takes the live oral vaccine and they shed some weakened virus particles in their body waste. Especially in areas where water sanitation is poor, an unvaccinated person can pick up the shed virus particles from the contaminated water. Once in the unvaccinated person’s body, the virus can replicate and (possibly) acquire mutations making it more virulent.
An inactivated (IPV) vaccine which can’t mutate or cause the disease has also been available since 1955. This vaccine can be given only as an injection, so it hasn’t been as easy to produce or administer worldwide. In the interest of eliminating this dreaded disease as fast as possible globally, the oral vaccine was preferred by most health authorities.
The oral vaccine hasn’t been used anywhere in the world since 2019, but this type of vaccine-derived polio has been showing up in small outbreaks. Based on genetic sequencing to identify the virus, this case in New York has been determined to be a revertant polio virus from the Sabin oral vaccine.
In New York, Rockland County will host polio vaccination clinics at the Pomona health complex on Friday and Monday. If you are concerned about yourself or a family member, contact your family physician.
[Featured image from CDC via Politico source article]