Understandably, these events provoked many questions: Why does a case of polio concern the authorities? What does it mean to find poliovirus in wastewater? Who should be concerned about getting the disease? If someone got the vaccine years ago, are they still protected now?
To understand more about this disease, which most people alive today have never experienced, I spoke with CNN medical analyst Dr. Leana Wen, an emergency physician and professor of health policy and management at the Milken Institute School of Public Health at George Washington University. She is also the author of “Lifelines: A Doctor’s Journey in the Fight for Public Health”.
CNN: So far, there has been only one documented case of paralysis due to poliovirus in New York. Why does a case concern health authorities?
Dr. AS Leana Wen: An August report from the CDC said that “even a single case of paralytic polio represents a public health emergency in the United States.” This is for two main reasons.
First, polio is a disease with the potential for very serious consequences. During its heyday in the 1940s and 1950s, polio resulted in tens of thousands of children becoming paralyzed every year. Thousands have died from the virus.
This changed with the introduction of highly effective vaccines – over 99% effective in protecting against paralytic polio. Thanks to mass vaccination campaigns, the last incidence of wild-type polio occurred in 1979 – and it was considered eliminated in the United States. The resurgence of such a disease, which can have such severe impacts, is a major threat.
Second, the single case of paralytic polio may be the tip of a large iceberg. Most cases of polio infection are asymptomatic and do not cause paralysis. Symptoms – which can include fatigue, fever and diarrhea – tend to be mild and can resemble those of other viruses. Public health officials are concerned that many other people may be infected with polio and unknowingly transmit it.
This is particularly concerning because Rockland County, where the recent crippling case of the virus was diagnosed, has a polio vaccination rate of just 60%. In some parts of the county, the vaccination rate is as low as 37%. These numbers are far below the threshold needed for herd immunity, and that means there are many individuals in the area who are vulnerable to polio infection and possible serious outcomes.
CNN: What does it mean that poliovirus was detected in the wastewater of five counties, including New York City?
Wen: Finding poliovirus in sewage means one of two things: that there are people actively infected with polio who are shedding the virus, or that the sign of the virus could be from people who have recently received the oral polio vaccine (OPV). OPV is no longer administered in the United States – since 2000, the version used in the US is the inactivated polio vaccine (IPV), which is injected – but other countries are still using OPV, and it is possible that travelers from these places are shedding vaccine virus.
In rare circumstances, weakened virus from people who have just received OPV can cause paralytic polio in unvaccinated individuals – which is one of the main reasons why OPV is no longer used in the US.
An additional point of concern is that a wastewater sample from Nassau County on Long Island was genetically linked to the case of paralytic polio identified in Rockland County. (The two counties are not adjacent, but approximately 40 miles apart.) This is further evidence of community spread that is going unnoticed.
CNN: How can people get polio?
Wen: Polio is an infectious disease that can be transmitted in a number of ways. One primary route is fecal-oral, which means someone can get polio if they come into contact with feces from an infected person. This can occur, especially in children, through placing objects such as toys contaminated with feces in the mouth.
Poliovirus can also be transmitted via the respiratory route – for example, if an infected person coughs or sneezes and these droplets land in their mouth. It is worth noting that vaccinated people can also contract polio and pass it on to others, although they are extremely well protected from serious illness.
CNN: Should New Yorkers be concerned about contracting polio?
Wen: Again, people vaccinated against polio are extremely well protected from paralytic polio and should not be concerned at this point. It should be noted, however, that while IPV is very good at preventing the most serious potential effects of the disease, people who have received the vaccine can still carry polio and pass it on to others. People at risk for serious outcomes are unvaccinated and incompletely vaccinated people, including children under age 6 who have not yet completed their polio vaccine series.
CNN: How many polio vaccines should someone get?
Wen: The CDC recommends that children receive four doses of IPV. The first is given at 2 months of age, the second at 4 months, the third between 6 and 18 months and the fourth between 4 and 6 years.
Adults who have never been vaccinated against polio should receive three doses of IPV. The first should be administered as soon as possible, the second one to two months later and the third six to 12 months after the second.
CNN: If someone got the vaccine years ago, are they still protected? Who should get a polio booster now?
Wen: Protection against serious illness remains strong for many years after immunization; it is believed to probably last a lifetime. There is no need for most vaccinated people to receive more doses.
However, if someone has not completed their original series of vaccines, they must receive the remaining doses. Some fully vaccinated people may also receive an additional lifetime booster of IPV in specific circumstances – for example, if they have direct contact with someone suspected of having polio or if they are healthcare workers at higher risk of exposure to people with the disease.
CNN: What if you’re not sure if you’ve been vaccinated? Let’s say you don’t remember getting the vaccine, and it’s been many years. Is there a blood test you can do to check anyway?
Wen: You can check with your primary care physician’s office or state health department to see if they have records of your immunizations. If they don’t, and there’s no other way to check — for example, asking parents or other relatives or caregivers — you should talk to your doctor about getting the full range of polio vaccines now. There is no blood test that can reliably detect whether you are fully vaccinated against polio.
CNN: What if you or your family members haven’t been vaccinated against poliovirus?
Wen: People who have not yet received any doses or are incompletely vaccinated should make sure they get the full series of polio vaccines right away. This is particularly important if they live in or around Rockland County, New York — but really everyone should keep up with their routine immunizations.
It was a tragedy decades ago that so many children were permanently paralyzed and even died of polio. This should not happen again, as we have vaccines so effective that they can prevent serious consequences of the disease.
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