The CDC used a precise scientific term when naming recent polio in the US as "vaccine-derived" in a September 13 media statement. But do people know what that means?
In late August, the US reported a case of paralytic polio in an unvaccinated adult in Rockland County, New York. This first case in the US since 2013 was concerning because it emerged in an area with especially low vaccination rates (around 60 percent, to the country’s average of 80 percent), and was still appearing in wastewater samples. The ratio of cases yielding paralysis per infection for these “type 2” polioviruses is 1:2000, which suggests the possibility of far more infected people. The US had eradicated polio transmission in 1979.
Now, the latest CDC announcement requires the utmost scientific literacy to be spread responsibly and well, to combat this rising threat. On September 13, the CDC confirmed that the polioviruses found in Rockland County are “vaccine-derived”: an accurate, but complex term to use when trying to promote increased vaccine uptake.
What it means, and what needs to be disseminated widely, is this:
- There are two forms of polio vaccine, oral and injection-based.
- The oral version had its benefits, because polio transmits through fecal matter into our sewage systems, and this vaccine followed the route of the original infection, allowing for increased communal protection against polio “in the wild”.
- But the oral version uses a weakened poliovirus, and once in several million doses, this virus regains “neurovirulence” (the ability to affect neurons) during its passage through the gut, creating an infection that risks paralysis and death.
- Because of this rare but extreme flaw, the US switched to the injection-based vaccine, IPV, in 2000. Other rich nations did likewise. Countries of lower means have not, because the oral vaccine is easier to store and administer.
- IPV, while safer for individual recipients, does not grant communal benefits, because it does not spread through our wastewater systems.
- If local immunity through vaccination were higher, this wouldn’t be a problem.
- But where vaccination rates are low, there are more opportunities for the weakened virus, when transmitted to our wastewater systems by anyone who received an oral vaccine, to mutate and spread through the unvaccinated.
- A country with no polio is thus still at risk, so long as the world has the disease.
- The CDC found enough genetic changes to the polioviruses in Rockland County wastewater, samples from the surrounding area, and the sample from the now-paralyzed young man, to meet the definition for circulating vaccine-derived poliovirus, or cVDPV.
- Low vaccination rates created this health crisis. Higher ones are needed to stop it.
Polio is a brutal disease, which the WHO declared eliminated in the Americas in 1994. Some people who lived through the worst wave of polio, in the 1950s, are still in wheelchairs and iron lungs today. The US now joins a list of 33 other countries with cVDPV: an active state of polio transmission, in need of immediate and collective redress. So get disseminating.